Question

Find all numbers for which the expression is undefined
t^3-3t/t^2-81

Answer 1

once again only when dividing by 0,
t^2-81=0
(t-9)(t+9)=0, so when t= 9 or -9 you have a problem

Answer 2

yep can't have a zero in the denominator or it's undefined

Answer 3

just factor like tutor did, then set it equal to zero