X8Y-3 = y5X5
why?, where does (x to the fifth power) come from?
i thought its like 2+(-3)=-1 so it would be X -1 power
I'm afraid I can't figure out what you mean...? (The apparent meaning of your posted expression cannot lead to the apparent meaning of the posted "answer", so something is wrong.)
Please use LaTeX formatting, or (which is simpler) standard web-safe formatting to clarify your meaning.
P.S. If you're needing a review of exponent rules, including how to work with negative powers, try here.