Factorise :
(i) a2−ab−3a+3b(ii) x2y−xy2+5x−5y(iii) a2−ab(1−b)−b3(iv) xy2+(x−1)y−1(v) (ax+by)2+(bx−ay)2(vi) ab(x2+y2)−xy(a2+b2)(vii) m−1−(m−1)2+am−a
(i) a2−ab−3a+3b=a(a−b)−3(a−b)=(a−b)(a−3)(ii) x2y−xy2+5x−5y=xy(x−y)+5(x−y)=(x−y)(xy+5)(iii) a2−ab(1−b)−b3=a2−ab+ab2−b3=a(a−b)+b2(a−b)=(a−b)(a+b)2(iv) xy2+(x−1)y−1=xy2+xy−y−1=xy(y+1)−1(y+1)=(xy−1)(y+1)(v) (ax+by)2+(bx−ay)2=a2x2+b2y2+2abxy+b2x2+a2y2−2abxy=a2x2+b2y2+b2x2+. y2−a2x2+a2y2+b2x2+b2y2−a2(x2+y2)+b2(x2+y2)=(x2+y2)(a2+b2)(vi) ab(x2+y2)−xy(a2+b2)=abx2+aby2−a2xy−b2xy=abx2−a2xy+aby2−b2xy=abx2−a2xy−b2xy+aby2=ax(bx−ay)−by(bx−ay)=(bx−ay)(ax−by)(vii) m−1−(m−1)2+am−a=(m−1)−(m−1)2+a(m−1)=(m−1)(1−(m−1)+a)=(m−1)(1−m+1+a)=(m−1)(2−m+a)