Question

Which is the correct cofunction identity for cos theta

A. csc(90° - theta)


B. sec(90° - theta)


C. sin(90° - theta)


D. cos(90° - theta)


E. tan(90° - theta)

Answer 1

Answer: Option 'C' is correct.

Explanation:

Since we have given that

`\cos \theta`

We need to find the correct cofunction identity for it.

Cofunction identities represent the relationship among the trigonometric functions.

The value of trigonometric function of an angle is equal to cofunction of its complement.

As we know that sine is a complement of cosine.

so, it becomes,

`\cos \theta=\sin(90^\circ-\theta)`

Hence, Option 'C' is correct.

Answer 2

C. sin(90° - θ)

Explanation:

A trig function of an angle equals the cofunction of the angle's complement.

The cofunction of cosine is sine, and the complement of θ is 90° - θ.

∴ cosθ = sin(90° - θ)