Division by zero, i.e., zero denominators, cause
an expression to be undefined.



That has a denominator 10x²-11, and the expression for f/g
will be undefined when the denominator 10x²-11 equals 0.

So solve 10x²-11 = 0 for the two values of x which cause
the denominator to be equal to zero, (making f/g undefined).

To do that:

Add 11 to both sides.  Divide both sides by 10 to get only
x² on the left.  Then use the square root principle with 
the ±.  That will give you two values when the denominator
equals 0 making f/g undefined.

Edwin