Question

What is the value of the expression (2x + y) (2x - y) when x = 4 and y = -5?

Answer 1

39

Explanation:

1. (2(4)-5)(2(4)+5)

2.(3)(13)

3.39

Answer 2

Explanation:

This is a difference of squares question. You should 64 = 25 = 39 Let's see if that happens.

Difference of squares

(2x - y) ( 2x + y) = 4x^2 - y^2

4(4)^2 - (5)^2

64 - 25 = 39

Now do the question exactly as it is written.

(2*4 - -5)(2*4 + -5)

(8 +5)(8 - 5)

3 * 13

39

They really do give the same answer.