The solution to 15 a2 − 1 = 5 2a − 2 is a = . the extraneous solution is a = .

For this case the correct expression is:
 15 / (a ^ 2 - 1) = 5 / (2a - 2)
 Rewriting we have:
 3 / (a ^ 2 - 1) = 1/2 (a - 1)
 6 / (a ^ 2 - 1) = 1 / (a - 1)
 6 (a - 1) = (a ^ 2 - 1)
 6 (a - 1) = (a-1) (a + 1)
 (a + 1) = 6
 a = 6-1
 a = 5
 
 The solution is:
 a = 5

That is the answer to your question