Let’s say that you are asked to find f(5/4) when f(x) = -x^2 – 4x + 7. This would take some work, but there’s an easier way of doing it on your graphing calculator.
1.) Press the Y= button. Enter -x^2 – 4x + 7 into the first line.
2.) Next, press 2ND, and then TRACE.
3.) Select the 1st option, “value,” and press ENTER.
4.) Since we are finding f(5/4), enter in 5/4 next to where it says “X=”. Press ENTER.
The calculator will give you the y-value on the graph where x = -4. This is the same thing as finding f(5/4). The answer you get is f(5/4) = .4375.
If need be, you can also use your TI-84 to convert this decimal into a fraction.
Simply pressing 2ND, MODE to go back to the home screen. Enter in the decimal, and then press MATH, ENTER, and then ENTER again. The answer you get is 7/16.
You can also find a table of values for this function by pressing 2ND, GRAPH. This table values only finds why values for integer values of x, however.
On your own, see if you can find f(-2/5) for f(x) = 10x^2 – 4x – 2.
Watch the video to see the answer!