assume that no variable equals 0
If the problem says a2 x
a6, then that is the same thing as having 2 a's being multiplied by each other, and then being multiplied by 6 a's, so
(a • a)(a • a • a • a • a • a) = a8.
In general when you are multiplying two numbers that have the same base, you can keep the base and add their exponents.
So a2 • a6 = a2+6 = a8.