chung minh rang` bieu thuc: M=(x+2 \frac{a}{b} x-1).[(x^2 \frac{a}{b} 2x+2) +1 ] - (8x +7 \frac{a}{b} 2x^2 -2) luon^ luon^ co gia tri ko be hon 2 voi moi gia tri cua x =/ +-1 :confused::confused::confused::confused: