Question

  

Answer 1

Lời giải:
$\cos x-\sin x=m-3$

$\Rightarrow (\cos x-\sin x)^2=(m-3)^2$

$\Leftrightarrow \cos ^2x+\sin ^2x-2\sin x\cos x=m^2-6m+9$

$\Leftrightarrow 1-2\sin x\cos x=m^2-6m+9$

$\Leftrightarrow \sin x\cos x=\frac{1-(m^2-6m+9)}{2}=\frac{-m^2+6m-8}{2}$