若x^2-kxy+9y^2满足a^2+2ab+b^2,则k=?

问题描述:

若x^2-kxy+9y^2满足a^2+2ab+b^2,则k=?

x^2-kxy+9y^2
=x^2-kxy +(3y)^2
=x^2-2*x*3y+(3y)^2
所以k=2*3=6