Giải thích các bước giải:
Ta có:
$(\sin x+\cos x-1)(\sin x-\cos x+1)$
$=(\sin x+(\cos x-1))(\sin x-(\cos x-1))$
$=\sin^2x-(\cos x-1)^2$
$=\sin^2x-(\cos^2x-2\cos x+1)$
$=\sin^2x-\cos^2x+2\cos x-1$
$=\sin^2x-\cos^2x+2\cos x-(\sin^2x+\cos^2x)$
$=-2\cos^2x+2\cos x$
$=2\cos x(1-\cos x)$
$\to \dfrac{\sin x+\cos x-1}{1-\cos x}=\dfrac{2\cos x}{\sin x-\cos x+1}$