Question

十字相乘x^2-2x=3（解方程）5x^2+7-6,3a^2-8a+4,2x^2+15x+7,7(x+y)^3-5(x+

Answer 1

x^2-2x=3

x^2-2x-3=0

(x-3)(x+1)=0

x1=3,x2=-1.

5x^2+7x-6=(x+2)(5x-3)

3a^2-8a+4=(a-2)(3a-2)

2x^2+15x+7=(x+7)(2x+1)

7(x+y)^3-5(x+y)^2-2(x+y)

=(x+y)[7(x+y)^2-5(x+y)-2]

=(x+y)[(x+y)-1][7(x+y)+2]

=(x+y)(x+y-1)(7x+7y+2)