Equation editor and matrices (and cases)

Here I have a case where I can’t insert matrices or cases into the Google document. Of course, the jibberish examples provided by Docx2Latex work fine, but as soon as I want to write my own formula, it doesn’t render them (it freezes at the insertion stage). Here is the case I want to write:

Xp = S. \cos{\beta}.\cos{\alpha} \
Xp = S. \cos{\beta}.\sin{\alpha} \
Xp = S. \cos{\beta}

and here is the picture:

Is it a bug? or an intended feature to force people to buy credits?