求几道一元二次方程的过程
(11)x^2+15x-54=0 x1=-18 x2=3
(12)x^2+11x+18=0 x1=-2 x2=-9
(13)x^2-9x+20=0 x1=4 x2=5
(14)x^2+19x+90=0 x1=-10 x2=-9
(15)x^2-25x+156=0 x1=13 x2=12
(16)x^2-22x+57=0 x1=3 x2=19
(17)x^2-5x-176=0 x1=16 x2=-11
(18)x^2-26x+133=0 x1=7 x2=19
(19)x^2+10x-11=0 x1=-11 x2=1
(20)x^2-3x-304=0 x1=-16 x2=19