Mixed font size and /tiny

Can I mix different font sizes in one Latex expression? Can I use /tiny, etc... to change font size? It seems that I don't but maybe Im doing it wrong.

something like:

In short. No.

If you find that system is using smaller fonts for parts of the equation, for example in a fraction, then you can use displaystyle to force it to be the same size as other text. But thats about the some of the adjustment allowed with standard LaTeX.

An example with:

\frac{\frac{1+2}{3}}{35}

which appears as:

You can make all the test style the same size with

\frac{\displaystyle \frac{1+2}{3}}{35}

which now appears as:

Beyond that we're not aware of any wany to change font sizes. Perhaps someone else can englighted us.