[tex]\frac{a^6}{a^4} = \frac{a\times a \times a \times a \times a \times a}{a \times a \times a \times a} = a \times a = a ^{6-4} = a^2[/tex]
If you started crossing the a's in the numerator and denominator, then you would be left with a x a
Hope that helped :)
