Question

prove that cos2x=cos^2x-sin^2x

Answer 1

Sure.

We know that, (this is the rule)
\(\normalsize\color{blue}{ \cos(a+b)=\cos(a)\cos(b)-\sin(a)\sin(b)}\)

So, when the a and b are same, (lets say that both "a" and "b" --- are "x"

\(\normalsize\color{blue}{ \cos(x+x)=\cos(x)\cos(x)-\sin(x)\sin(x)}\)

that is the same as, \(\normalsize\color{blue}{ \cos(x+x)=\cos^2(x)-\sin^2(x)}\)

Answer 2

No, I won't type now.. :P

Answer 3

\(\large\tt \color{black}{\text{u can use formula}}\)

\(\large\tt \color{blue}{cos(A+B)=cosAcosB-sinAsinB}\)