9(a+b)^2-4(a-b)^2.x^2(m-1)(1-m)^2.

9(a+b)^2-4(a-b)^2.x^2(m-1)(1-m)^2.
9(a+b)^2-4(a-b)^2.x^2(m-1)(1-m)^2.

9(a+b)^2-4(a-b)^2.x^2(m-1)(1-m)^2.
9(a+b)^2-4(a-b)^2
=[3(a+b)+2(a-b)][3(a+b)-2(a-b)]
=(3a+3b+2a-2b)(3a+3b-2a+2b)
=(5a+b)(a+5b)
x^2(m-1)^2-(1-m)^2
=x^2(m-1)^2-(m-1)^2
=(m-1)^2(x^2-1)
=(x-1)(x+1)(m-1)^2