方法一、配方法：x^2-x-90=0(x-1/2)^2-90-1/4=0(x-1/2)^2=90+1/4(x-1/2)^2=361/4x-1/2=±19/2x1=1/2+19/2=10x2=1/2-19/2=-9方法二、十字相乘法：x^2-x-90=0(x-10)(x+9)=0x=10或x=-6
x²-x-90=0(x+9)(x-10)=0x+9=0或x-10=0x=-9或x=10
