Question

If cos2A=11/25, show that cosA=6/5√2​

Answer 1

Answer:

it is not I think...

Step-by-step explanation:

Using the identity

$\cos(2a) = 2 \cos^2(a) - 1$

We can solve:

$2 \cos^2(a) - 1 = \frac{11}{25}$

$2 \cos^2(a) = \frac{36}{25}$

$\cos^2(a) = \frac{18}{25}$

$\cos(a) = \sqrt \frac{18}{25}$

$\cos(a) = \sqrt{ 2 \cdot \frac{3^2}{5^2} }= \frac35 \sqrt 2$

So whoever asked the question forgot the factor 2!!!

Or did I miss anything??