Toán Chung minh rang: sinx. × cos mũ 3- cosx.sin mũ 3 x=1 phần 4 sin 4x 04/08/2021 By Valerie Chung minh rang: sinx. × cos mũ 3- cosx.sin mũ 3 x=1 phần 4 sin 4x
$\begin{array}{l} \sin x{\cos ^3}x – \cos x{\sin ^3}x\\ = \sin x\cos x\left( {{{\cos }^2}x – {{\sin }^2}x} \right)\\ = \dfrac{1}{2}.\sin 2x.\cos 2x = \dfrac{1}{4}\sin 4x \end{array}$ Trả lời
$\begin{array}{l} \sin x{\cos ^3}x – \cos x{\sin ^3}x\\ = \sin x\cos x\left( {{{\cos }^2}x – {{\sin }^2}x} \right)\\ = \dfrac{1}{2}.\sin 2x.\cos 2x = \dfrac{1}{4}\sin 4x \end{array}$