[OS X TeX] A little help needed (math formula problem)

[Joe Java]

Hello TeX group,

I wrote a webpage for testing MathML support in a browser. 
I used TeX as the "gold standard" for mathematical representation.
See:
https://eyeasme.com/Joe/MathML/MathML_browser_test
Click on any equation to see the code that generated it.

The problem is "Test 3" gives errors but displays correctly.  
I would like to have the "0" in "Test 3" be larger and bold, 
but then the multiple errors are just too much and I get no 
displayed result.  How do I rewrite the code so I get no errors?

Comments and suggestions on improving the TeX coding for 
any of the examples would be appreciated.

    Joe