For which value of x is undefined?

'Undefined' is usually another name for 'infinity', which always pops up when you try to divide by zero.

In this one, there's a fraction, and you're asked:  "When is the fraction undefined ?"

If the denominator of the fraction is ever zero, then that's nothing but the old
"division by zero", which is forbidden, not permitted, and undefined.

The denominator of the fraction is  x² + 3x + 2 .  Can that ever be zero ?
It might be easier to see if you factor it:
(x + 2) · (x + 1) = 0
This equation is true if x=-2 OR x=-1 . 
Either way, the denominator of the fraction is zero. 
So those are the values of 'x' for which the fraction is undefined.