Dane jest wyrażenie 

$ab+a-b-1$

A.

$\left(a-1\right)\left(b-1\right)=ab-a-b+1\ne ab+a-b-1$

B.

$\left(a+1\right)\left(b-1\right)=ab-a+b-1\ne ab+a-b-1$

C.

$\left(\mathbf{a}-1\right)\left(\mathbf{b}+1\right)=\mathbf{a}\mathbf{b}+\mathbf{a}-\mathbf{b}-1$

D.

$\left(a+1\right)\left(b+1\right)=ab+a+b+1\ne ab+a-b-1$

 

Odp. C.