x^2+x=240解：x^2+x-240=0(x+16)(x-15)=0x+16=0，x-15=0则x1=-16x2=15
x²+x-240=0(x+16)(x-15)=0x=-16或15
x²+x=240x²+x-240=0(x+16)(x-15)=0x1=-16，x2=15
