tolong nomor 9 nya ditulisin cara dan jawabannya ya.. makasih

A = x + a
B = x + b

A x B
= x² + ax + bx + ab

Keterangan
= x (x) + a (x) + b (x) + a (b)
= x² + ax + bx + ab

(x+a)(x+b)
= (x. x) + (x.b) + (a.x) +(a.b)
= x²+xb+xa+ab