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 
