Answer:
a)

The function
is not defined at
because these values result in a zero denominator, leading to division by zero, which is undefined in mathematics.
Step-by-step explanation:
The given function is
. To determine where the function is not defined, we need to identify values of
that make the denominator equal to zero. In this case, the denominator is
. Setting this expression equal to zero, we find:
![\[ x^2 - 25 = 0 \]](https://img.qammunity.org/2024/formulas/mathematics/high-school/gngojlfn63o3560n3wthccdhuyk5n2fy19.png)
Factoring the quadratic expression, we get \
. This equation has solutions
Therefore, the function is not defined at

In summary, the function
is not defined at
. This is because these values make the denominator zero, leading to division by zero, which is undefined in mathematics.