TDSM 2.15
From The Data Science Design Manual Wikia
The derivative of [math]f(x) = \log_a x[/math] ([math]x \gt 0[/math]) is [math]\frac{\ln{a}}{x} \gt 0[/math] [math]\forall x \gt 0[/math] so [math]\log_a x[/math] is an increasing function.
With [math]x \lt 1[/math] we have [math]f(x) \lt f(1) = \log_a 1 = 0[/math] (proved)
