Question

初三数学：一元二次方程

（1）x（x-15)=3(x+5)
(2) (x-1)(x-2)=3
可以快点嘛，在线

Answer 1

x(x-15)=3(x+5)
x²-15x=3x+15
x²-18x=15
x²-18x+81=15+81
（x-9)²=96
x-9=±4√6
x1=9+4√6, x2=9-4√6

(x-1)(x-2)=3
x²-2x-x+2=3
x²-3x-1=0
b²-4ac=9+4=13
x=(3±√13)/2
x1=(3+√13)/2, x2=(3-√13)/2

Answer 2

1. x^2 - 15x = 3x + 15

   x^2 - 18x - 15 = 0

   x = [18 ±√(18^2 + 4*15)]/2 = 9 ± 4√6

2. x^2 - 3x + 2 = 3

   x^2 - 3x -1 = 0

   x = [3 ±√(3^2 + 4)]/2 = (3 ±√13)/2

Answer 3

(1) x（x-15)=3(x+5)

x²-15x=3x+15
x²-18x-15=0
(2) (x-1)(x-2)=3

x²-3x+2=3
x²-3x-1=0