Exapnd cos ( 70 ° ) using a double angle identity.

Answer 1

The Double Angle Identities for cosine:

1) cos(2x)=cos²(x)-sin²(x)

2) cos(2x)=2cos²(x)-1

3) cos(2x)=1-2sin²(x)

Since you were given cos(70), let's consider x=35, so that way 2x=70.

cos(70)

=cos(2*35)

=cos(2x) (with x=35)

Let's use the first identity listed above.

=cos²(35)-sin²(35)

This is one way to expand cos(70) using a double angle identity.

Hope this helps! :)

Answer 2

You have 3 choices to expand it.

cos^2(35) - sin^2(35) or

2cos^2(35) - 1 or

1 - 2sin^2(35)