The tutor explains the idea of odd function vs even function.

An odd function is one that gives the opposite output for -x as for x:

f(x) odd, then f(-x) = -f(x)

x³ and sinx are both odd functions:

(-2)³=-8, while (2)³=8

sin(-1.2) = -0.932, sin(1.2) = 0.932

An even function gives the same output for -x as for x:

f(x) even, then f(-x) = f(x)

x² and cosx are even functions:

(-5)²=25=(5)²

cos(1.3)=0.267=cos(-1.3)

Most functions are neither odd nor even.

Source:

Larson, Roland E. and Robert Hostetler. Calculus, 3rd ed. Toronto: DC Heath and Company, 1989.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.