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Popular Trigonometry >

(6.3)/(cos(27))

Solution

\frac{6.3}{cos ( 2 7 ^{\circ} )}

Solution

\frac{63 ( - 5 - 5 + 2 2 ) ( 3 - 5 ) 2 5 - 5 + 4}{20}

Decimal

7.07065 \dots

Solution steps

\frac{6.3}{cos ( 2 7 ^{\circ} )}

= \frac{\frac{63}{10}}{cos ( 2 7 ^{\circ} )}

Simplify

= \frac{63}{10 cos ( 2 7 ^{\circ} )}

Rewrite using trig identities:

cos (2 7^{\circ}) = \frac{1 + cos ( 5 4 ^{\circ} )}{2}

cos (2 7^{\circ})

Write

cos (2 7^{\circ})

cos (\frac{5 4 ^{\circ}}{2})

= cos (\frac{5 4 ^{\circ}}{2})

Use the Half Angle identity:

cos (\frac{θ}{2}) = \frac{1 + cos ( θ )}{2}

Use the Double Angle identity

cos (2 θ) = 2 cos^{2} (θ) - 1

Substitute

θ

with

\frac{θ}{2}

cos (θ) = 2 cos^{2} (\frac{θ}{2}) - 1

Switch sides

2 cos^{2} (\frac{θ}{2}) = 1 + cos (θ)

Divide both sides by

2

cos^{2} (\frac{θ}{2}) = \frac{( 1 + cos ( θ ) )}{2}

Square root both sides

Choose the root sign according to the quadrant of

\frac{θ}{2}

range [0, 9 0^{\circ}] [9 0^{\circ}, 18 0^{\circ}] [18 0^{\circ}, 27 0^{\circ}] [27 0^{\circ}, 36 0^{\circ}] quadrant I II III I V sin positive positive negative negative cos positive negative negative positive

cos (\frac{θ}{2}) = \frac{( 1 + cos ( θ ) )}{2}

= \frac{1 + cos ( 5 4 ^{\circ} )}{2}

= \frac{63}{10 \frac{1 + c o s ( 5 4 ^{\circ} )}{2}}

Simplify

= \frac{63 ( 5 2 - 5 2 cos ( 5 4 ^{\circ} ) ) 1 + cos ( 5 4 ^{\circ} )}{50 - 50 cos ^{2} ( 5 4 ^{\circ} )}

Rewrite using trig identities:

cos (5 4^{\circ}) = \frac{2 5 - 5}{4}

cos (5 4^{\circ})

Rewrite using trig identities:

sin (3 6^{\circ})

cos (5 4^{\circ})

Use the following identity:

cos (x) = sin (9 0^{\circ} - x)

= sin (9 0^{\circ} - 5 4^{\circ})

Simplify

= sin (3 6^{\circ})

= sin (3 6^{\circ})

Rewrite using trig identities:

\frac{2 5 - 5}{4}

sin (3 6^{\circ})

Show that:

cos (3 6^{\circ}) - sin (1 8^{\circ}) = \frac{1}{2}

Use the following product to sum identity:

2 sin (x) cos (y) = sin (x + y) - sin (x - y)

2 cos (3 6^{\circ}) sin (1 8^{\circ}) = sin (5 4^{\circ}) - sin (1 8^{\circ})

Show that:

2 cos (3 6^{\circ}) sin (1 8^{\circ}) = \frac{1}{2}

Use the Double Angle identity:

sin (2 x) = 2 sin (x) cos (x)

sin (7 2^{\circ}) = 2 sin (3 6^{\circ}) cos (3 6^{\circ})

sin (7 2^{\circ}) sin (3 6^{\circ}) = 4 sin (3 6^{\circ}) sin (1 8^{\circ}) cos (3 6^{\circ}) cos (1 8^{\circ})

Divide both sides by

sin (3 6^{\circ})

sin (7 2^{\circ}) = 4 sin (1 8^{\circ}) cos (3 6^{\circ}) cos (1 8^{\circ})

Use the following identity:

sin (x) = cos (9 0^{\circ} - x)

sin (7 2^{\circ}) = cos (9 0^{\circ} - 7 2^{\circ})

cos (9 0^{\circ} - 7 2^{\circ}) = 4 sin (1 8^{\circ}) cos (3 6^{\circ}) cos (1 8^{\circ})

cos (1 8^{\circ}) = 4 sin (1 8^{\circ}) cos (3 6^{\circ}) cos (1 8^{\circ})

Divide both sides by

cos (1 8^{\circ})

1 = 4 sin (1 8^{\circ}) cos (3 6^{\circ})

Divide both sides by

2

\frac{1}{2} = 2 sin (1 8^{\circ}) cos (3 6^{\circ})

Substitute

\frac{1}{2} = 2 sin (1 8^{\circ}) cos (3 6^{\circ})

\frac{1}{2} = sin (5 4^{\circ}) - sin (1 8^{\circ})

sin (5 4^{\circ}) = cos (9 0^{\circ} - 5 4^{\circ})

\frac{1}{2} = cos (9 0^{\circ} - 5 4^{\circ}) - sin (1 8^{\circ})

\frac{1}{2} = cos (3 6^{\circ}) - sin (1 8^{\circ})

Show that:

cos (3 6^{\circ}) + sin (1 8^{\circ}) = \frac{5}{4}

Use the factorization rule:

a^{2} - b^{2} = (a + b) (a - b)

a = cos (3 6^{\circ}) + sin (1 8^{\circ})

(cos (3 6^{\circ}) + sin (1 8^{\circ}))^{2} - (cos (3 6^{\circ}) - sin (1 8^{\circ}))^{2} = ((cos (3 6^{\circ}) + sin (1 8^{\circ})) + (cos (3 6^{\circ}) - sin (1 8^{\circ}))) ((cos (3 6^{\circ}) + sin (1 8^{\circ})) - (cos (3 6^{\circ}) - sin (1 8^{\circ})))

Refine

(cos (3 6^{\circ}) + sin (1 8^{\circ}))^{2} - (cos (3 6^{\circ}) - sin (1 8^{\circ}))^{2} = 2 (2 cos (3 6^{\circ}) sin (1 8^{\circ}))

Show that:

2 cos (3 6^{\circ}) sin (1 8^{\circ}) = \frac{1}{2}

Use the Double Angle identity:

sin (2 x) = 2 sin (x) cos (x)

sin (7 2^{\circ}) = 2 sin (3 6^{\circ}) cos (3 6^{\circ})

sin (7 2^{\circ}) sin (3 6^{\circ}) = 4 sin (3 6^{\circ}) sin (1 8^{\circ}) cos (3 6^{\circ}) cos (1 8^{\circ})

Divide both sides by

sin (3 6^{\circ})

sin (7 2^{\circ}) = 4 sin (1 8^{\circ}) cos (3 6^{\circ}) cos (1 8^{\circ})

Use the following identity:

sin (x) = cos (9 0^{\circ} - x)

sin (7 2^{\circ}) = cos (9 0^{\circ} - 7 2^{\circ})

cos (9 0^{\circ} - 7 2^{\circ}) = 4 sin (1 8^{\circ}) cos (3 6^{\circ}) cos (1 8^{\circ})

cos (1 8^{\circ}) = 4 sin (1 8^{\circ}) cos (3 6^{\circ}) cos (1 8^{\circ})

Divide both sides by

cos (1 8^{\circ})

1 = 4 sin (1 8^{\circ}) cos (3 6^{\circ})

Divide both sides by

2

\frac{1}{2} = 2 sin (1 8^{\circ}) cos (3 6^{\circ})

Substitute

2 cos (3 6^{\circ}) sin (1 8^{\circ}) = \frac{1}{2}

(cos (3 6^{\circ}) + sin (1 8^{\circ}))^{2} - (cos (3 6^{\circ}) - sin (1 8^{\circ}))^{2} = 1

Substitute

cos (3 6^{\circ}) - sin (1 8^{\circ}) = \frac{1}{2}

(cos (3 6^{\circ}) + sin (1 8^{\circ}))^{2} - (\frac{1}{2})^{2} = 1

Refine

(cos (3 6^{\circ}) + sin (1 8^{\circ}))^{2} - \frac{1}{4} = 1

Add

\frac{1}{4}

to both sides

(cos (3 6^{\circ}) + sin (1 8^{\circ}))^{2} - \frac{1}{4} + \frac{1}{4} = 1 + \frac{1}{4}

Refine

(cos (3 6^{\circ}) + sin (1 8^{\circ}))^{2} = \frac{5}{4}

Take the square root of both sides

cos (3 6^{\circ}) + sin (1 8^{\circ}) = \pm \frac{5}{4}

cos (3 6^{\circ})

cannot be negative

sin (1 8^{\circ})

cannot be negative

cos (3 6^{\circ}) + sin (1 8^{\circ}) = \frac{5}{4}

Add the following equations

cos (3 6^{\circ}) + sin (1 8^{\circ}) = \frac{5}{2}

((cos (3 6^{\circ}) + sin (1 8^{\circ})) + (cos (3 6^{\circ}) - sin (1 8^{\circ}))) = (\frac{5}{2} + \frac{1}{2})

Refine

cos (3 6^{\circ}) = \frac{5 + 1}{4}

Square both sides

(cos (3 6^{\circ}))^{2} = (\frac{5 + 1}{4})^{2}

Use the following identity:

sin^{2} (x) = 1 - cos^{2} (x)

sin^{2} (3 6^{\circ}) = 1 - cos^{2} (3 6^{\circ})

Substitute

cos (3 6^{\circ}) = \frac{5 + 1}{4}

sin^{2} (3 6^{\circ}) = 1 - (\frac{5 + 1}{4})^{2}

Refine

sin^{2} (3 6^{\circ}) = \frac{5 - 5}{8}

Take the square root of both sides

sin (3 6^{\circ}) = \pm \frac{5 - 5}{8}

sin (3 6^{\circ})

cannot be negative

sin (3 6^{\circ}) = \frac{5 - 5}{8}

Refine

sin (3 6^{\circ}) = \frac{\frac{5 - 5}{2}}{2}

= \frac{\frac{5 - 5}{2}}{2}

Simplify

= \frac{2 5 - 5}{4}

= \frac{2 5 - 5}{4}

= \frac{63 ( 5 2 - 5 2 \frac{2 5 - 5}{4} ) 1 + \frac{2 5 - 5}{4}}{50 - 50 ( \frac{2 5 - 5}{4} ) ^{2}}

Simplify

\frac{63 ( 5 2 - 5 2 \frac{2 5 - 5}{4} ) 1 + \frac{2 5 - 5}{4}}{50 - 50 ( \frac{2 5 - 5}{4} ) ^{2}} : \frac{63 ( - 5 - 5 + 2 2 ) ( 3 - 5 ) 2 5 - 5 + 4}{20}

\frac{63 ( 5 2 - 5 2 \frac{2 5 - 5}{4} ) 1 + \frac{2 5 - 5}{4}}{50 - 50 ( \frac{2 5 - 5}{4} ) ^{2}}

50 (\frac{2 5 - 5}{4})^{2} = \frac{25 ( 5 - 5 )}{4}

50 (\frac{2 5 - 5}{4})^{2}

(\frac{2 5 - 5}{4})^{2} = \frac{5 - 5}{2 ^{3}}

(\frac{2 5 - 5}{4})^{2}

Apply exponent rule:

(\frac{a}{b})^{c} = \frac{a ^{c}}{b ^{c}}

= \frac{( 2 5 - 5 ) ^{2}}{4 ^{2}}

Apply exponent rule:

(a \cdot b)^{n} = a^{n} b^{n}

(2 5 - 5)^{2} = (2)^{2} (5 - 5)^{2}

= \frac{( 2 ) ^{2} ( 5 - 5 ) ^{2}}{4 ^{2}}

(2)^{2} : 2

Apply radical rule:

a = a^{\frac{1}{2}}

= (2^{\frac{1}{2}})^{2}

Apply exponent rule:

(a^{b})^{c} = a^{b c}

= 2^{\frac{1}{2} \cdot 2}

\frac{1}{2} \cdot 2 = 1

\frac{1}{2} \cdot 2

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{1 \cdot 2}{2}

Cancel the common factor:

2

= 1

= 2

= \frac{2 ( 5 - 5 ) ^{2}}{4 ^{2}}

(5 - 5)^{2} : 5 - 5

Apply radical rule:

a = a^{\frac{1}{2}}

= ((5 - 5)^{\frac{1}{2}})^{2}

Apply exponent rule:

(a^{b})^{c} = a^{b c}

= (5 - 5)^{\frac{1}{2} \cdot 2}

\frac{1}{2} \cdot 2 = 1

\frac{1}{2} \cdot 2

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{1 \cdot 2}{2}

Cancel the common factor:

2

= 1

= 5 - 5

= \frac{2 ( 5 - 5 )}{4 ^{2}}

Factor

4^{2} : 2^{4}

Factor

4 = 2^{2}

= (2^{2})^{2}

Simplify

(2^{2})^{2} : 2^{4}

(2^{2})^{2}

Apply exponent rule:

(a^{b})^{c} = a^{b c}

= 2^{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= 2^{4}

= 2^{4}

= \frac{2 ( 5 - 5 )}{2 ^{4}}

Cancel the common factor:

2

= \frac{5 - 5}{2 ^{3}}

= 50 \cdot \frac{5 - 5}{2 ^{3}}

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{( 5 - 5 ) \cdot 50}{2 ^{3}}

Factor

50 : 5^{2} \cdot 2

Factor

50 = 5^{2} \cdot 2

= \frac{5 ^{2} \cdot 2 ( 5 - 5 )}{2 ^{3}}

Cancel the common factor:

2

= \frac{5 ^{2} ( 5 - 5 )}{2 ^{2}}

5^{2} = 25

= \frac{25 ( 5 - 5 )}{2 ^{2}}

2^{2} = 4

= \frac{25 ( 5 - 5 )}{4}

= \frac{63 ( - 5 2 \frac{2 5 - 5}{4} + 5 2 ) \frac{2 5 - 5}{4} + 1}{50 - \frac{25 ( 5 - 5 )}{4}}

52 \frac{2 5 - 5}{4} = \frac{5 5 - 5}{2}

52 \frac{2 5 - 5}{4}

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{2 5 - 5 \cdot 5 2}{4}

2 5 - 5 \cdot 52 = 10 5 - 5

2 5 - 5 \cdot 52

Apply radical rule:

a a = a

22 = 2

= 5 \cdot 2 5 - 5

Multiply the numbers:

5 \cdot 2 = 10

= 10 5 - 5

= \frac{10 5 - 5}{4}

Cancel the common factor:

2

= \frac{5 5 - 5}{2}

= \frac{63 ( - \frac{5 5 - 5}{2} + 5 2 ) \frac{2 5 - 5}{4} + 1}{50 - \frac{25 ( 5 - 5 )}{4}}

1 + \frac{2 5 - 5}{4} = \frac{4 + 2 5 - 5}{2}

1 + \frac{2 5 - 5}{4}

Join

1 + \frac{2 5 - 5}{4} : \frac{4 + 2 5 - 5}{4}

1 + \frac{2 5 - 5}{4}

Convert element to fraction:

1 = \frac{1 \cdot 4}{4}

= \frac{1 \cdot 4}{4} + \frac{2 5 - 5}{4}

Since the denominators are equal, combine the fractions:

\frac{a}{c} \pm \frac{b}{c} = \frac{a \pm b}{c}

= \frac{1 \cdot 4 + 2 5 - 5}{4}

Multiply the numbers:

1 \cdot 4 = 4

= \frac{4 + 2 5 - 5}{4}

= \frac{4 + 2 5 - 5}{4}

Apply radical rule:

n \frac{a}{b} = \frac{n a}{n b},

assuming

a \geq 0, b \geq 0

= \frac{4 + 2 5 - 5}{4}

4 = 2

4

Factor the number:

4 = 2^{2}

= 2^{2}

Apply radical rule:

n a^{n} = a

2^{2} = 2

= 2

= \frac{4 + 2 5 - 5}{2}

= \frac{63 \cdot \frac{2 5 - 5 + 4}{2} ( - \frac{5 5 - 5}{2} + 5 2 )}{50 - \frac{25 ( 5 - 5 )}{4}}

Join

50 - \frac{25 ( 5 - 5 )}{4} : \frac{75 + 25 5}{4}

50 - \frac{25 ( 5 - 5 )}{4}

Convert element to fraction:

50 = \frac{50 \cdot 4}{4}

= \frac{50 \cdot 4}{4} - \frac{25 ( 5 - 5 )}{4}

Since the denominators are equal, combine the fractions:

\frac{a}{c} \pm \frac{b}{c} = \frac{a \pm b}{c}

= \frac{50 \cdot 4 - 25 ( 5 - 5 )}{4}

Multiply the numbers:

50 \cdot 4 = 200

= \frac{200 - 25 ( 5 - 5 )}{4}

Expand

200 - 25 (5 - 5) : 75 + 255

200 - 25 (5 - 5)

Expand

- 25 (5 - 5) : - 125 + 255

- 25 (5 - 5)

Apply the distributive law:

a (b - c) = ab - a c

a = - 25, b = 5, c = 5

= - 25 \cdot 5 - (- 25) 5

Apply minus-plus rules

- (- a) = a

= - 25 \cdot 5 + 255

Multiply the numbers:

25 \cdot 5 = 125

= - 125 + 255

= 200 - 125 + 255

Subtract the numbers:

200 - 125 = 75

= 75 + 255

= \frac{75 + 25 5}{4}

= \frac{63 \cdot \frac{2 5 - 5 + 4}{2} ( - \frac{5 5 - 5}{2} + 5 2 )}{\frac{75 + 25 5}{4}}

Multiply

63 (52 - \frac{5 5 - 5}{2}) \frac{4 + 2 5 - 5}{2} : \frac{63 ( - 5 5 - 5 + 10 2 ) 2 5 - 5 + 4}{4}

63 (52 - \frac{5 5 - 5}{2}) \frac{4 + 2 5 - 5}{2}

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{4 + 2 5 - 5 \cdot 63 ( 5 2 - \frac{5 5 - 5}{2} )}{2}

Join

52 - \frac{5 5 - 5}{2} : \frac{10 2 - 5 5 - 5}{2}

52 - \frac{5 5 - 5}{2}

Convert element to fraction:

52 = \frac{5 \cdot 2 \cdot 2}{2}

= \frac{5 2 \cdot 2}{2} - \frac{5 5 - 5}{2}

Since the denominators are equal, combine the fractions:

\frac{a}{c} \pm \frac{b}{c} = \frac{a \pm b}{c}

= \frac{5 2 \cdot 2 - 5 5 - 5}{2}

Multiply the numbers:

5 \cdot 2 = 10

= \frac{10 2 - 5 5 - 5}{2}

= \frac{63 \cdot \frac{- 5 5 - 5 + 10 2}{2} 2 5 - 5 + 4}{2}

Multiply

4 + 2 5 - 5 \cdot 63 \cdot \frac{10 2 - 5 5 - 5}{2} : \frac{63 ( - 5 5 - 5 + 10 2 ) 2 5 - 5 + 4}{2}

4 + 2 5 - 5 \cdot 63 \cdot \frac{10 2 - 5 5 - 5}{2}

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{( 10 2 - 5 5 - 5 ) 4 + 2 5 - 5 \cdot 63}{2}

= \frac{\frac{63 ( - 5 5 - 5 + 10 2 ) 2 5 - 5 + 4}{2}}{2}

Apply the fraction rule:

\frac{\frac{b}{c}}{a} = \frac{b}{c \cdot a}

= \frac{( 10 2 - 5 5 - 5 ) 4 + 2 5 - 5 \cdot 63}{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{63 ( - 5 5 - 5 + 10 2 ) 2 5 - 5 + 4}{4}

= \frac{\frac{63 ( - 5 5 - 5 + 10 2 ) 2 5 - 5 + 4}{4}}{\frac{75 + 25 5}{4}}

Divide fractions:

\frac{\frac{a}{b}}{\frac{c}{d}} = \frac{a \cdot d}{b \cdot c}

= \frac{( 10 2 - 5 5 - 5 ) 4 + 2 5 - 5 \cdot 63 \cdot 4}{4 ( 75 + 25 5 )}

Cancel the common factor:

4

= \frac{( 10 2 - 5 5 - 5 ) 4 + 2 5 - 5 \cdot 63}{75 + 25 5}

Factor

(102 - 5 5 - 5) 4 + 2 5 - 5 \cdot 63 : 315 (22 - 5 - 5) 4 + 2 5 - 5

(102 - 5 5 - 5) 4 + 2 5 - 5 \cdot 63

Factor

102 - 5 5 - 5 : 5 (22 - 5 - 5)

102 - 5 5 - 5

Rewrite as

= 5 \cdot 22 - 5 5 - 5

Factor out common term

5

= 5 (22 - 5 - 5)

= 5 (22 - 5 - 5) 4 + 2 5 - 5 \cdot 63

Refine

= 315 (22 - 5 - 5) 4 + 2 5 - 5

= \frac{315 ( 2 2 - 5 - 5 ) 4 + 2 5 - 5}{75 + 25 5}

Factor

75 + 255 : 25 (3 + 5)

75 + 255

Rewrite as

= 25 \cdot 3 + 255

Factor out common term

25

= 25 (3 + 5)

= \frac{315 ( 2 2 - 5 - 5 ) 4 + 2 5 - 5}{25 ( 3 + 5 )}

Cancel the common factor:

5

= \frac{63 ( - 5 - 5 + 2 2 ) 2 5 - 5 + 4}{5 ( 3 + 5 )}

Rationalize

\frac{63 ( - 5 - 5 + 2 2 ) 2 5 - 5 + 4}{5 ( 3 + 5 )} : \frac{63 ( 3 - 5 ) ( - 5 - 5 + 2 2 ) 2 5 - 5 + 4}{20}

\frac{63 ( - 5 - 5 + 2 2 ) 2 5 - 5 + 4}{5 ( 3 + 5 )}

Multiply by the conjugate

\frac{3 - 5}{3 - 5}

= \frac{63 ( - 5 - 5 + 2 2 ) 2 5 - 5 + 4 ( 3 - 5 )}{5 ( 3 + 5 ) ( 3 - 5 )}

5 (3 + 5) (3 - 5) = 20

5 (3 + 5) (3 - 5)

Expand

(3 + 5) (3 - 5) : 4

(3 + 5) (3 - 5)

Apply Difference of Two Squares Formula:

(a + b) (a - b) = a^{2} - b^{2}

a = 3, b = 5

= 3^{2} - (5)^{2}

Simplify

3^{2} - (5)^{2} : 4

3^{2} - (5)^{2}

3^{2} = 9

3^{2}

3^{2} = 9

= 9

(5)^{2} = 5

(5)^{2}

Apply radical rule:

a = a^{\frac{1}{2}}

= (5^{\frac{1}{2}})^{2}

Apply exponent rule:

(a^{b})^{c} = a^{b c}

= 5^{\frac{1}{2} \cdot 2}

\frac{1}{2} \cdot 2 = 1

\frac{1}{2} \cdot 2

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{1 \cdot 2}{2}

Cancel the common factor:

2

= 1

= 5

= 9 - 5

Subtract the numbers:

9 - 5 = 4

= 4

= 4

= 5 \cdot 4

Expand

5 \cdot 4 : 20

5 \cdot 4

Distribute parentheses

= 5 \cdot 4

Multiply the numbers:

5 \cdot 4 = 20

= 20

= 20

= \frac{63 ( - 5 - 5 + 2 2 ) ( 3 - 5 ) 2 5 - 5 + 4}{20}

= \frac{63 ( - 5 - 5 + 2 2 ) ( 3 - 5 ) 2 5 - 5 + 4}{20}

= \frac{63 ( - 5 - 5 + 2 2 ) ( 3 - 5 ) 2 5 - 5 + 4}{20}

Popular Examples

cos(arctan(3/4)-arccos(7/25))