# With exams looming, people might come to tutoring with questions about their calculators: What does it do (besides the obvious)? How can it really help me? The tutor offers a handy hint about the CASIO fx-991ES.

Some exams don’t allow the use of just any calculator. Make sure, as a student, you know which one(s) you can use. If you need to buy a different one for the exam, pick it up as soon as you can: familiarity with your calculator is key.

For those allowed to use the CASIO* fx-991ES,* its derivative function might be useful. As far as I can see (and would expect anyway), it doesn’t seem to do symbolic derivatives, but will find the value of the derivative at a specific ** x** value.

**Example:**

Find the value of

d/dx (x^0.5-1)/(sinx +2), x=5

Even those who can confidently evaluate this derivative are likely not excited about doing it.

Well, here’s how to have the CASIO *fx-991ES* do it for you:

- I was in MATH mode when I did this. (That’s shift setup 1).
- Press shift∫. Enter the derivative expression: (√x-1)/(sin(x)+2)
*(Note: it autobrackets with*sin.) Use the arrows at left and right of the replay to move around as needed;eg, to get out of the radical sign. - After your expression is entered, arrow over to x= and enter your desired value at which to evaluate the derivative. (x=5, in this case).
- Press =. The screen may go blank for a few seconds while the calculator computes the answer. Then, you should be greeted with a restatement of the expression and the answer across the bottom: -0.1087192572, in this case.

I don’t have to explain to calculus students how convenient this function can be:)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.