1. Cho A = \frac{5x-y}{3x+7}-\frac{3y-2x}{2y-7}. Tính A với 2x - y =7
A = \frac{5x-y}{3x+7}-\frac{3y-2x}{2y-7}
= \frac{(3x+2x)-y}{3x+7}-\frac{-(2x-3y)}{2y-7}
= \frac{3x+(2x-y)}{3x+7}-\frac{-(2x-y-2y)}{2y-7}
= \frac{3x+7}{3x+7}-\frac{-[(2x-y)-2y)}{2y-7}
= \frac{3x+7}{3x+7}-\frac{-(7-2y)}{2y-7}...