expression undefined

1/(2x^2 - 50)

Could you please show me how to do this? thank you

Undefined means the expression cannot be evaluated with a unique finite value.

Examples of undefined values are ∞, ∞, 1/0, 0/0. In the case where we restrict ourselves to real values, then sqrt(-3) is also considered undefined.

We note that f(x)=1/(2x^2 - 50) can be evaluated for every x except when the denominator is zero, then f(x) evaluates to 1/0 which is undefined.
When f(x) is undefined, then
2x²-50=0
x²=25
or x=±5.
So
f(x) is defined in ℝ (all real values) except ±5.