Factorise: 1+2ab−(a2+b2)
1+2ab−(a2+b2)=1+2ab−a2−b2=1−a2+2ab−b2=12−(a2−2ab+b2)=12−(a−b)2since [a2−2ab+b2=(a−b)2]=[1+(a−b)][1−(a−b)]since [a2−b2=(a+b)(a−b)] =(1+a−b)(1−a+b)
Factorise: 25−a2−b2−2ab