# Finding Reciprocal Functions SEC, CSC, COT on TI-30XA

First, you may want to refresh your memory of the regular trig functions:

Now, let’s find $\csc \frac{5\pi }{4}$.
If we look it up on WolframAlpha, we find that it equals $-\sqrt{2}$, or, roughly, $-1.4142$.

To get this answer on the TI-30XA, first remember that $\csc$ is equal to $\frac{1}{\sin }$.

So, what we’re looking for could be expressed as $\frac{1}{\sin \frac{5\pi }{4}}$. Once we know this, we can type $5\cdot \pi$ into the TI-30XA.

This gives us ~15.7. (Make sure you’re in radian mode. If not, press the DRG button — located by the 2nd button, upper-left — until you see RAD appear in small letters on the screen.)

Now, we can divide 15.7 by 4. This gives us 3.925. If we take the $\sin$ of this (by pressing the “sin” button while 3.925 is displayed), we get $-0.7$. IF we divide 1 by $-0.7$, we get $-1.43$. As you can see, this is close to the correct value. You can get a more exact value by using the STO function on the calculator. [Press “STO” while a number is displayed on screen and then the number “1” on the keypad. Press the clear button (ON/C). Now, press RCL and the number “1” on the keypad. Your saved value should appear.]

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