Is the set \mathbb{z} a group under the operation a*b = a - b + ab ? justify your answer.

Step-by-step explanation:

Given that *is the binary operation in the sets of integers.

closure: a-b+ab is again an integer belongs to Z.  Hence closure is true.

Associativity:

The two are not equal.  Hence this cannot be a group as associtiavity does not hold good.

2/3

step-by-step explanation:

- (2, -7)

- lines r and s and lines t and u must be parallel