x^2+(7-x)^2-25=0 =x^2-7x+12=0 =(x-3)(x-4)=0 =x1=3,x2=4 中x^2-7x+12=0是怎样化简得到的

问题描述:

x^2+(7-x)^2-25=0 =x^2-7x+12=0 =(x-3)(x-4)=0 =x1=3,x2=4 中x^2-7x+12=0是怎样化简得到的

x²+(7-x)²-25=0
x²+49-14x+x²-25=0
2x²-14x+24=0
2 (x²-7x+12)=0
x²-7x+12=0
(x-3)(x-4)=0
(x-3)=0
(x-4)=0

x1=3,x2=4

x²+7²-2×7×x+x²-25=2x²-14x+24=x²-7x+12

首先说明:你不能这样连续等!这种表达方式错误~
x^2+(7-x)^2-25=0 =x^2-7x+12=0 =(x-3)(x-4)=0 =x1=3,x2=4
x^2+(7-x)^2-25=0
x^2+49-14x+x^2-25=0
2x^2-14x+24=0
x^2-7x+12=0
……

(7-x)^2 =49-14x+ x^2