4x(x+3)=-34x^2+12x+3=0(4x+1)(x+3)=04x+1=0 或 x+3=04x=-1x1=-1/4x2=-33x^2-3x-1=0 x^2-x-1/3=0x^2-x-1/3+1/4-1/4=0(x-1/2)^2-7/12=0[x-1/2+√（7/12）][x-1/2-√（7/12）]=0x-1/2+√（7/12）=0 或 x-1/2-√（7/12...