Problem: Indicate in which one of the following equations yyy is neither directly nor inversely proportional to xxx:
Answer Choices:
A. x+y=0x+y=0x+y=0 B. 3xy=103 x y=103xy=10 C. x=5yx=5 yx=5y D. 3x+y=103 x+y=103x+y=10 E. xy=3\dfrac{x}{y}=\sqrt{3}yx=3
Solution:
(A)(A)(A), (B)(B)(B), (C)(C)(C), and (E)(E)(E) are of the form y=kxy=k xy=kx or xy=kx y=kxy=k, but (D)\boxed{(D)}(D) is not.