计算3（x-7）²=x²-49

计算3（x-7）²=x²-49
计算3（x-7）²=x²-49

计算3（x-7）²=x²-49
3（x-7）²=x²-49
3(x-7)^2=(x-7)(x+7)
当X-7=0时,x=7
当x-7不等于0时
3(x-7)=x+7
3x-21=x+7
2x=28
x=14
所以x1=7.x2=14

3（x-7）=(x+7)(x-7)
3(x-7)-(x+7)(x-7)=0
[3-(x+7)](x-7)=0
(10-x)(x-7)=0
x=10或x=7

3（x-7）²=x²-49
3(x²-14x+49)=x²-49
2x²-42x+4*49=0
x²-21+98=0
(x-14)(x-7)=0
x=14或 x=7