Question

Question #c2854

Answer 1

See explanation.

Explanation:

A formula for `cos2A` states that:

`cos2A=cos^2A-sin^2A`

This can be transformed to:

`cos2A=cos^2A-(1-cos^2A)`

`cos2A=2cos^2A-1`

Using the last formula the initial expression can be written as:

`2cos^2 13-1=cos 26`