Sender: "Leanne Hickey" Subject: inverses of functions heres the question.... Let f(x) = 2x2 -3x + 2. Find f-1(4) given the fact that f(2) = 4. So the question is finding the inverse of 4, he said it's easier than it looks. thanks alot Hi Leanne, Functions behave like the square root button on a calculator. You give it a number and it gives you an answer. If you give the square root function the number 16 it gives you the answer 4. For your function f(x) = 2x2 -3x + 2 if you give it the input number 2 it gives you the answer 4 and if you give it the input number 3 it gives you the answer 11.    Inverse functions work like Jeopardy, you give it the answer and it tells you the input number. You tell f-1 that the answer was 4 and it replies that the input number was 2. You tell it that the answer was 11 and it tells you that the input number was 3. That is f-1(4) = 2 and f-1(11) = 3.    You do have to take some care with inverses of functions as two different input numbers might give the same answer. If you check you will see that f(-1/2) is also 4 so f-1(4) might be -1/2. Cheers, Penny Go to Math Central