(1)x²+4x-9=2x-11
x²+2x+1=-1
(x+1)²=-1
x+1=±i
x=-1±i
(2)x(x+4)=8x+12
x²+4x=8x+12
x²-4x+4=16
(x-2)²=16
x-2=±4
x=-2或x=6