How to show the + symbol in an equation that is generated by https://render.githubusercontent.com for github-pages?

I can't seem to get the "+" symbol to appear:

<img src="https://render.githubusercontent.com/render/math?math={\color{black} \large \sigma = f(\mu) = a\mu^2 + b\mu + c} ">   Eqn(2)

It is giving me this wrong result. The appearance I desire is this correct appearance.

Solution

Quoting a comment by @Jishan in this answer

Anyone using this method, because + is an escape character in URI, use %2B to render +.