If x + y = 3 and x – y = 5, then x2 – y2 = A. 4 B. 8 C. 15 D. 16 E

1.	If x + y = 3 and x – y = 5, then x2 – y2 = A. 4 B. 8 C. 15 D. 16 E. 64?
Answer» Step-by-step explanation: x + y = 3 x - y = 5 ----------------- 2x = 8 add together x = 4 y = -1 x^2 - y^2 = 16 - 1 = 15. Answer = C. Alternative way (x+y) (x -y) = x^2 + xy - xy - y^2 = x^2 - y^2. Hence, 3 * 5 = 15. Answer = C

If x + y = 3 and x – y = 5, then x2 – y2 = A. 4 B. 8 C. 15 D. 16 E. 64?

Answer»

Step-by-step explanation:

x + y = 3

x - y = 5

-----------------

2x = 8 add together

x = 4

y = -1

x^2 - y^2 = 16 - 1 = 15.

Answer = C.

Alternative way

(x+y) (x -y) = x^2 + xy - xy - y^2 = x^2 - y^2.

Hence,

3 * 5 = 15.

Answer = C