因为|m+6|>罩搜答=0 (m+2n)²>=0 所以要使|m+6|+(m+2n)²=0 只能 m=-6 n=3代入得:(4m²-2mn-5n²)-(5m²-6mn+2n²)物慧漏派 =-m²+4mn-7n² =-171