Question

I need help with my exam practice homework . Question 3 please

Answer 1

we have that

The double angles formula is equal to

`\cos (2\theta)=\cos ^2(\theta)-\sin ^2(\theta)`

and remember that

`\begin{gathered} \sin ^2(\theta)+\cos ^2(\theta)=1 \\ \cos ^2(\theta)=1-\sin ^2(\theta) \end{gathered}`

therefore

substitute in the original expression

`\begin{gathered} \cos (2\theta)=1-\sin ^2(\theta)-\sin ^2(\theta) \\ \cos (2\theta)=1-2\sin ^2(\theta) \end{gathered}`

therefore

The third option is incorrect