已知m,n是方程x-2x-1=0的两根,且(7m-14m+a)(3n-6n-7)=8,求a的值
问题描述:
已知m,n是方程x-2x-1=0的两根,且(7m-14m+a)(3n-6n-7)=8,求a的值
答
由题意知m-2m-1=0;故7(m-2m-1)=0,即7m-14m-7=0 同理3n-6n-3=0,∴(7m-14m+a)(3n-6n-7) =(7m-14m-7+7+a)(3n-6n-3-4) =(7+a)×(-4)=8 ∴a=-9