3x^2+9x+10=643x^2+9x-54=0x^2+3x-18=0(x+6)(x-3)=0x=-6或x=3 4x^2+2x-1=0（2x)^2+2x+1/4=5/4(2x+1/2)^2=5/42x+1/2=±√5/2x=（√5-1）/4或x=（-1-√5）/43x(x-5)=4x-203x^2-19x+20=0(x-5)(3x-4)=0x=5或x=4/3...