Which expression represents a difference of squares?

A. 81 − 49y^2

B. 4x^2 − 16x

C. t^2 + 100

D. 25k − 64

A.    81 - 49y²

Step-by-step explanation:

The triangle that represent a difference of squares is A.

It is easily recognize by looking at the numbers , the number  gives a perfect square and the variable y is also squared

That is 9² = 81                   and         7² = 49  and

Also the sign in-between them must me a negative sign, when the expression consist of the above, then it gives a different of square.

81 - 49y²

9² - 7²y²

(9 - 7y)(9 +7y)

Lets open back the parenthesis to check our answer

(9 - 7y)(9 +7y)

9(9+7y) -7y(9+7y)

81 +63y -63y -49y²

81 - 49y²

1/800 is the right answer