Here's some hints in case they're still needed.

For 3.17: Let y = sqrt(x) and try writing out the binomial theorem for (y+2)^(2n+1). Note if x has an integer power, then y is raised to an even power. What happens if we let y = 1 and y = -1 in the binomial theorem?

For 3.20: For this one as well, write out the binomial theorem. Note that each term can be simplified to +- (10 choose k) * (a power of 2) * (a power of x) for some k = 0 to 10. Since (10 choose k) is always an integer, consider when (a power of 2) is rational.