My Solution:If 8xy³ + 8x³y = (2x²y²)/2^-³, what is the value of xy?
- y > x
- x < 0
8xy³ + 8x³y = (2x²y²) / 2^-³
2³xy³ + 2³x³y = 2^4 * x² * y²
2³(xy³ + x³y) = 2^4 * x² * y² ; div both sides by 2³
xy³ + x³y = 2x²y²
xy³ + x³y - 2x²y² = 0
xy(y² + x² - 2xy) = 0
xy(x - y)(x - y) = 0
xy(x - y)² = 0
Statement 1: y > x means that x - y < 0, which means that x - y cannot be 0, thus xy = 0.
Sufficient.
Statement 2: x < 0. No info about y.
Insufficient.
I chose answer choice A, which is the correct answer.
My question though, is about the factoring that I did. In the book, the explanation factors it like this:
(xy)(y - x)² = 0.
How do we know which should be be subtracted from which? In this particular case, it works out to be the same, because the result is squared.
Has anyone seen an official question where the order of the x and y matters?
Will it ever matter?
Thanks,
--Rishi
Note: Mistyped RHS of problem. Fixed from (2x²y²)/2^-³ to be (2x²y²)/2^-².