Question

已知m,n是方程x²-2x-1=0的两根,且(7m²-14m+a)(3n²6n-7)=8,

Answer 1

mn是方程x^2-2x-1=0的二根,则有m^2-2m-1=0和n^2-2n-1=0

那么有3n^2-6n-7=3(n^2-2n)-7=3*1-7=-4

所以有7m^2-14m+a=8/(-4)=-2

7(m^2-2m)+a=-2

7*1+a=-2

a=-9