6(a+b)^2+40(a+b)(a-b)+25(a-b)^2
=[(2(a+b)+5(a-b)][3(a+b)+5(a-b)]
=(2a+2b+5a-5b)(3a+3b+5a-5b)
=(7a-3b)(8a-2b)
=2(7a-3b)(4a-b)