Question

cos 2x = cos²x - sin² x​

Answer 1

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Answer 2

$\sf{ \underline{ \underline{Question}}}$

• Prove $\sf{Cos2x\:=\: \ Cos^{2}x- \ Sin^{2}x}$

$\sf{ \underline{ \underline{Solution}}}$

$\sf{L.H.S}$

$\sf{Cos2x\:=\:Cos(x+x)}$

$\tt\boxed{ Cos(A+B)\:=\: Cos A Cos B- Sin A Sin B}$

$\mapsto\sf{Cos x \times Cos x- Sin x \times Sin x}$

$\mapsto\sf{\ Cos^{2}x- \ Sin^{2}x}$

$\sf{L.H.S\:=\:R.H.S}$

$\sf{ \underline{ \underline{Hence\:\: Proved}}}$