Question

t^3-6t over t^2-81

find all numbers in which the rational expression is undefined.

Answer 1

Dividing anything by 0 results in an undefined number
So the denominator should be 0

t^2-81=0
t^2=81
t=9

Answer 2

t = -9 also works


So t = 9 or t = -9 make the expression undefined