Following the instructions on Irreducible representation, MathJax works on Blogger.

I typed

1

$\cos^2\theta-\sin^2\theta=\cos 2\theta$

and here’s the result: $\cos^2\theta-\sin^2\theta=\cos 2\theta$

Antoher equation:

This time, the equation is in display mode.

How about the inline verbatim environment? Googling “mathjax verbatim”, we have

according to $\rm \TeX$ Commands available in MathJax by Dr. Carol JVF Burns. Nevertheless, it only works in display mode.¹

Finally, let’s get some equations numbered, just like an example on the MathJax CDN.