The last one which you were asking where the b came from I typed the wrong problem sorry.

Question

the problem is 49-a^2b^2
Is the answer: (7+ab)-(7ab)

Answer 1

(7-ab)(7+ab)

the difference of two squares
(sqrt first + sqrt second)(sqrt first - sqrt second)

Answer 2

Check these by multiplying them out.

Answer 3

How about answering your own question.

will I get 49-a^2b^2 if I simplify (7+ab)-(7ab) ??

now try (7 + ab)(7 - ab)

Answer 4

Thank you now I understand how to check them to see if there right. Thanks Damon, and thanks Reiny.