Question

Demonstrații :
a) cos x cos 2x cos 4x = sin 8 x supra 8 sin x,​

Answer 1

a) inmultim ambele parti cu 8sin(x), ca sa scapam de fractie

$8\sin(x)\cos(x)\cos(2x)\cos(4x) = \sin(8x) \\ 4\sin(2x)\cos(2x)\cos(4x) = \sin(8x) \\ 2\sin(4x)\cos(4x) = \sin(8x) \\ \sin(8x) = \sin(8x) \\\iff \: adevarat \\ \\ formula : \\\boxed{ 2\sin(x)\cos(x) = \sin(2x)}$