x2+x(a+b)+ab is equal to
(x-a)(x+b)
(x+a)(x+b)
(b+a)(x+x)
(x+ax+b)
Multiply the terms. We get
(x+a)(x+b)=x2+bx+ax+ab=x2+x(a+b)+ab
x2 + (a + b)x + ab can be factorised as ______ .