CMR tam giác ABC vuông (hơi khó ạ)

V

vy000

$\sin A-\sin(A-B)\sin C+\cos B =\dfrac32$
<=> $\sin A-\sin(A-B)\sin(A+B)+\cos B=\dfrac32$
<=> $\sin A + \dfrac{\cos 2A}2-\dfrac{\cos 2B}2 + \cos B=\dfrac32$
<=> $\sin A-\sin^2A-\cos^2B+\cos B=\dfrac12$
ok ^^
 
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