What is the value of cos(-i) ?

The value of cos(-i) is (e^2+1)/(2e)

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cos(-i)

Solution

cos (- i)

Solution

\frac{e ^{2} + 1}{2 e}

Decimal Notation

1.54308 \dots

Solution steps

cos (- i)

Use the following property:

cos (- x) = cos (x)

cos (- i) = cos (i)

= cos (i)

Rewrite using trig identities:

cos (0) cosh (1) - i sin (0) sinh (1)

cos (i)

Use the following identity:

cos (a + bi) = cos (a) cosh (b) - i sin (a) sinh (b)

= cos (0) cosh (1) - i sin (0) sinh (1)

= cos (0) cosh (1) - i sin (0) sinh (1)

Use the following trivial identity:

sin (0) = 0

sin (0)

sin (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} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{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} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

= cos (0) cosh (1) - i 0 \cdot sinh (1)

= cos (0) cosh (1) - i 0 \cdot sinh (1)

Simplify

= cos (0) cosh (1)

Use the following trivial identity:

cos (0) = 1

cos (0)

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}

= 1

Rewrite using trig identities:

cosh (1) = \frac{e ^{2} + 1}{2 e}

cosh (1)

Use the Hyperbolic identity:

cosh (x) = \frac{e ^{x} + e ^{- x}}{2}

= \frac{e ^{1} + e ^{- 1}}{2}

\frac{e ^{1} + e ^{- 1}}{2} = \frac{e ^{2} + 1}{2 e}

\frac{e ^{1} + e ^{- 1}}{2}

Apply rule

a^{1} = a

e^{1} = e

= \frac{e + e ^{- 1}}{2}

Apply exponent rule:

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

= \frac{e + \frac{1}{e}}{2}

Join

e + \frac{1}{e} : \frac{e ^{2} + 1}{e}

e + \frac{1}{e}

Convert element to fraction:

e = \frac{ee}{e}

= \frac{ee}{e} + \frac{1}{e}

Since the denominators are equal, combine the fractions:

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

= \frac{ee + 1}{e}

ee + 1 = e^{2} + 1

ee + 1

ee = e^{2}

ee

Apply exponent rule:

a^{b} \cdot a^{c} = a^{b + c}

ee = e^{1 + 1}

= e^{1 + 1}

Add the numbers:

1 + 1 = 2

= e^{2}

= e^{2} + 1

= \frac{e ^{2} + 1}{e}

= \frac{\frac{e ^{2} + 1}{e}}{2}

Apply the fraction rule:

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

= \frac{e ^{2} + 1}{e 2}

= \frac{e ^{2} + 1}{2 e}

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

Simplify

= \frac{e ^{2} + 1}{2 e}

Popular Examples

cos(0)-cos(pi)

cos (0) - cos (π)

arccos(0.02)

arccos (0.02)

arccos(0.07)

arccos (0.07)

cos(1)pi

cos (1) π

arctan(12/19)

arctan (\frac{12}{19})

Frequently Asked Questions (FAQ)

What is the value of cos(-i) ?
The value of cos(-i) is (e^2+1)/(2e)