已知x为实数,且满足(x²+3x)²+3(x²+3x)-18=0.则x²+3x的值为____________

已知x为实数,且满足(x²+3x)²+3(x²+3x)-18=0.则x²+3x的值为____________
已知x为实数,且满足(x²+3x)²+3(x²+3x)-18=0.则x²+3x的值为____________

已知x为实数,且满足(x²+3x)²+3(x²+3x)-18=0.则x²+3x的值为____________
(x²+3x)²+3(x²+3x)-18=0
替换法,将x²+3x看成整体
设t=x²+3x
t²+3t-18=0
十字相乘得
(t+6)(t-3)=0
t=-6或t=3
x²+3x=-6时
x²+3x+6=0
Δ