Đáp án:
VT= $\frac{sin2a-2sin^{2}a}{sin2a-2cos^{2}a}$
= $\frac{2sinacosa-2(1-cos^{2}a)}{2sinacosa-2(1-sin^{2}a)}$
= $\frac{2(sinacosa- 1+cos^{2}a)}{2(sinacosa-1+sin^{2}a)}$
= $\frac{sinacosa- sin^{2}a}{sinacosa-cos^{2}a}$
= $\frac{-sina( sina-cosa)}{cos( sina-cosa)}$ = $\frac{-sina}{cosa}$
= -tana = VP