We are given the equality
and told to solve for a. That is, we should apply mathematical operations on both sides of the equality so we "isolate" variable a on one side of the equality. We start by multiplying both sides by a, so we get
Now, we subtract 2a from both sides. We get
We can factor on the left side a as a common factor, so we get
Finally, we divide by (g-2) on both sides, so we get