Question

当k取什么值时,多项式x的2次方+3kxy-3y的平方+1/3xy-8中不含xy项?

Answer 1

x^2 +3kxy-3y^2 +(1/3)xy-8

=x^2 +[3k+(1/3)]xy-3y^2 -8

因不含xy项,则：

3k+(1/3)=0

即 3k=-1/3

即 k=-1/9