For what real values of a is the expression (a + 3)/(a^3 - a) undefined? List your answers in increasing order separated by commas.
When the denominator is = 0 it is undefined
a^3 - a = 0
a^3 = a
a^2 = a
a = ±1
This is when the expression has to equal (a + 3)/0
a^3 - a = 0 = a(a+1)(a-1)
So it's undefined when a is -1 and 1.