Factorization a ^ 2 + 2Ab + B ^ 2-3a-3b-4

Factorization a ^ 2 + 2Ab + B ^ 2-3a-3b-4

a^2+b^2+2ab-3a-3b-4
=(a+b)^2-3(a+b)-4
=(a+b-4)(a+b+1)