Question

factorise
1+2ab-(a^2+b^2)

Answer 1

-1-2ab+(a^2+b^2)
(a+b)^2-1
(a+b+1)(a+b-1)

Answer 2

1+2ab-(a"2+b"2)
=1 -(a"2+b"2-2ab)
=1- (a-b)"2
={1-(a-b)} {1+(a-b)}