What is the value of 2cos(-pi/3) ?

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2cos(-pi/3)

2 cos (- \frac{π}{3})

1

Solution steps

2 cos (- \frac{π}{3})

Rewrite using trig identities:

cos (- \frac{π}{3}) = \frac{1}{2}

cos (- \frac{π}{3})

Use the following property:

cos (- x) = cos (x)

cos (- \frac{π}{3}) = cos (\frac{π}{3})

= cos (\frac{π}{3})

Use the following trivial identity:

cos (\frac{π}{3}) = \frac{1}{2}

cos (\frac{π}{3})

cos (x)

periodicity table with

2 πn

cycle:

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

= \frac{1}{2}

= \frac{1}{2}

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

Simplify

2 \cdot \frac{1}{2} : 1

2 \cdot \frac{1}{2}

Convert element to fraction:

2 = \frac{2}{1}

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

Cross-cancel:

2

= 1

= 1

25 \cdot cos (4 5^{\circ})

\frac{10}{cos ( 5 1 ^{\circ} )}

tan (- \frac{5 π}{2})

arcsin (0.45) + arccos (0.45) + arctan (0.45)

1 - sin^{2} (π)