若x=m,y=n是方程组2x+y=8,x-3y=1的解,求7n(m一3n)的平方-2(3n-m)3次
2019-04-12
若x=m,y=n是方程组2x+y=8,x-3y=1的解,求7n(m一3n)的平方-2(3n-m)
3次
优质解答
m-3n=x-3y=1;
3n-m=-(x-3y)=-1;
7n(m-3n)^2-2(3n-m)=7n+2=7y+2;
解方程组得y=6/7;
故7n(m-3n)^2-2(3n-m)=8
m-3n=x-3y=1;
3n-m=-(x-3y)=-1;
7n(m-3n)^2-2(3n-m)=7n+2=7y+2;
解方程组得y=6/7;
故7n(m-3n)^2-2(3n-m)=8