Rút gọn B = 2sin2x - 1/ sin2x - sinx × cosx

$B=\dfrac{2\sin2x-1}{2\sin x\cos x-\sin x\cos x}$

$=\dfrac{2.2\sin x\cos x-1}{\sin x\cos x}$

$=4-\dfrac{1}{\sin x\cos x}$

$=4-\dfrac{\sin^2x+\cos^2x}{\sin x\cos x}$

$=4-\dfrac{\sin^2x}{\sin x\cos x}-\dfrac{\cos^2x}{\sin x\cos x}$

$=4-\tan x-\cot x$