Question. What is the value of sum 3/4 + 9/16 + 27/64 + ... ? (The sum is infinite, and each term is 3/4 of the previous term.) Be careful. The sum does not start with 1.
Answer. If the sum started with 1, you would get 1/(1-3/4) = 4. Now just subtract the missing 1, giving 3.