(m-n)^2-14(m-n)+49
=(m-n)^2-2*7(m-n)+7^2
=(m-n-7)^2还有两题 帮下忙 我追加x平方-x-6 x平方-y平方-4x+4x^2-x-6 =x^2-(3-2)-2*3 =(x-3)(x+2) x^2-y^2-4x+4 =x^2-4x+4+y^2 =(x-2)^2-y^2 =(x-2+y)(x-2-y) =(x-2+y)(x-y-2)