How that each of these pairs of functions are of the same order

how that each of these pairs of functions are of the same order.

a) 3x + 7, x
b) 2x² + x − 7, x²
c) ⌊x + 1/2⌋, x
d) log(x² + 1), log₂ x
e) log₁₀ x, log₂ x