Question

Find the value of cos[-7π/3]
​

Answer 1

Answer:

cos(7π3) is just cos(2π+π3) .

Since cos(2π)=cos0 , cos2π=1 .

Go π3 ( 60° ) past that, and

you'll have cos(7π3)=cos(420°)=cos(60°) .

Answer 2

$\bf \: cos \left( - \frac{ 7\pi}{3} \right) = \frac{1}{2}$

Given:

• $\cos \left( \frac{ - 7\pi}{3} \right)$

To find:

• Find the value of trigonometric expression.

Solution:

Concept/formula to be used:

1. $\bf cos( - \theta) = cos( \theta)$
2. $\bf cos( 2\pi + \theta) = cos( \theta)$

Step 1:

Simplify the expression.

Apply formula 1.

$\cos \left( \frac{ - 7\pi}{3} \right) = \cos \left( \frac{ 7\pi}{3} \right)$

Step 2:

Simplify the expression.

$\cos \left( \frac{ 7\pi}{3} \right) =\cos \left(2\pi + \frac{ \pi}{3} \right)$

$\cos \left(2\pi + \frac{ \pi}{3} \right) =\cos \left( \frac{ \pi}{3} \right)$

The value of $\cos \left( \frac{ \pi}{3} \right) = \frac{1}{2}$

Thus,

$\bf cos \left( - \frac{ 7\pi}{3} \right) = \frac{1}{2}$

Learn more:

1) Value of cos[π/6 + cos⁻¹(- 1/2)] is.....,Select Proper option from the given options.

(a) - √3/2

(b) √3-1/2√2

(c) √5-1/4...

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2) The period of cos x sin (pi/4-x) is

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