If 8x + 8y = 18 and x2 - y2 = - , what is the value of 2x - 2y ?
A. -
B. -
C.
D.
Answer:A
If 8x + 8y = 18 and x2 - y2 = - , what is the value of 2x - 2y ?
A. - B. - C. D.
Explanation: A Start by simplifying 8x + 8y = 18 by dividing each term by 8: x + y = or : x + y = . The second equation provided in the question can be factored: x2 - y2 is the same as (x + y)(x - y), so the second equation can also be written (x + y)(x - y) = - . Since you know that x + y = , you can rewrite the second equation as (x - y) = - . Multiply both sides by : : x - y = - ( ) or x - y = - . Since the question asks for the value of 2x - 2y, simply multiply everything by 2: 2(x - y) = 2(- ) = - , which is (A).