Question

How do you prove cos(90°-a) = sin(a)?

Answer 1

See the Proof in Explanation Section.

Explanation:

We will use the following Expansion Formula :

`cos(A-B)=cosAcosB+sinAsinB`.

Let `A=90^@, and =a`. Therefore.

`cos(90^@-a)=cos90^@cosa+sin90^@sina`.

Here, we have, `cos90^@=0, sin90^@=1`.

`:. cos(90^@-a)=sina`.