M-4<0 M<42|X1*X2|=3|X1-X2|4X1方X2方=9(X1-X2)方=9[(X1+X2)方-4X1X2]9(X1+X2)方-36X1X2-4X1方X2方=09(2M+4)方-36(M-4)-4(M-4)方=09(4M方+16M+16)-36M+144-4(M方-8M+16)=032M方+140M+224=08M方+35M+56=035*35-4*8*56<0 无解呀 题目应该有错 方法就是这样了