Question

恒等变形4 ,急设x+2z=3y,试跑那段x^2-9y^2+4z^2+4xz的值是不是定值如果是定值,求出它的值,否则,

Answer 1

0么!

x+2z=3y

则：x+2z-3y=0

式：x^2-9y^2+4z^2+4xz

=x^2+4xz+4z^2-9y^2

=(x+2z)^2-(3z)^2

=(x+2z+3z)(x+2z-3y)

=0