If 0 < y < x, which statement must be true?

10

When simplified (x^-1 + y^-1)^-1 is equal to

11

If 8^x+1 = 64, what is the value of 3^2x+1?

13

If x is a positive real number and x² = 2, then x³ =

14

If (2³)² = 4^x, then 3^x =