Toán Gíup mình với ạ. Cmr cos3a+sin2a-cosa/2-2cos^2a-sina 13/09/2021 By Clara Gíup mình với ạ. Cmr cos3a+sin2a-cosa/2-2cos^2a-sina
$\dfrac{\cos3a-\cos a+\sin2a}{2-2\cos^2a-\sin a}$ $=\dfrac{-2\sin2a.\sin a+\sin2a}{2(1-\cos^2a)-\sin a}$ $=\dfrac{-2\sin2a.\sin a+\sin2a}{2\sin^2a-\sin a}$ $=\dfrac{\sin2a(-2\sin a+1)}{\sin a(2\sin a-1)}$ $=\dfrac{-\sin2a}{\sin a}$ $=\dfrac{-2\sin a\cos a}{\sin a}$ $=-2\cos a$ Trả lời
$\dfrac{\cos3a-\cos a+\sin2a}{2-2\cos^2a-\sin a}$
$=\dfrac{-2\sin2a.\sin a+\sin2a}{2(1-\cos^2a)-\sin a}$
$=\dfrac{-2\sin2a.\sin a+\sin2a}{2\sin^2a-\sin a}$
$=\dfrac{\sin2a(-2\sin a+1)}{\sin a(2\sin a-1)}$
$=\dfrac{-\sin2a}{\sin a}$
$=\dfrac{-2\sin a\cos a}{\sin a}$
$=-2\cos a$