# Why is graph undefined in desmos? [closed]

For the equation $$x\sqrt{200-x^2}$$, when I insert $$\sqrt{200}$$ for $$x$$, desmos says the output is undefined. But how can this be? The output is zero algebraically.

## closed as off-topic by postmortes, Adrian Keister, Paul Frost, mihaild, Parcly TaxelJul 6 at 8:07

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question is not about mathematics, within the scope defined in the help center." – postmortes, Paul Frost, mihaild, Parcly Taxel
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• It must be an issue with desmos. I tried different values instead of 200 and instead of 0 it gives me "undefined", "0" or supersmall number – Mihail Jul 5 at 11:12

As a guess though: when desmos calculates $$\sqrt{200}$$ it will round that to some precision (say 15 decimal places) and when it squares it again, it may use just that rounded number. In which case, the result could be slightly larger than $$200$$ so that it then has to try and take the square root of a negative number (e.g. $$\sqrt{(200-200.00000000000191)}$$) and that's what's giving you "undefined" as your answer.
It is a rounding error issue: in this Desmos graph you see that the radicand is slightly negative: $$f(\sqrt{200}) = −2.842170943×10^{−14}$$. This happens due to limited precision of floating point numbers.