we have that
The double angles formula is equal to
[tex]\cos (2\theta)=\cos ^2(\theta)-\sin ^2(\theta)[/tex]
and remember that
[tex]\begin{gathered} \sin ^2(\theta)+\cos ^2(\theta)=1 \\ \cos ^2(\theta)=1-\sin ^2(\theta) \end{gathered}[/tex]
therefore
substitute in the original expression
[tex]\begin{gathered} \cos (2\theta)=1-\sin ^2(\theta)-\sin ^2(\theta) \\ \cos (2\theta)=1-2\sin ^2(\theta) \end{gathered}[/tex]
therefore
The third option is incorrect
