# [SOLVED] help with inverse trig functions

• Apr 5th 2009, 05:31 PM
lsnyder
[SOLVED] help with inverse trig functions
okay i keep gettin these off-the-wall answers and am now starting to get fustrated because I got these other 30 right except these 2. so can someone please help me, I'd really appreciate it.

Evaluate each of the inverse trig functions in radians rounded to 4 decimal places

Problem 1

https://webwork.uncc.edu/webwork2_fi...0ba0ba3bb1.png

Problem2https://webwork.uncc.edu/webwork2_fi...c393e51c81.png
• Apr 5th 2009, 05:59 PM
Mush
Quote:

Originally Posted by lsnyder
okay i keep gettin these off-the-wall answers and am now starting to get fustrated because I got these other 30 right except these 2. so can someone please help me, I'd really appreciate it.

Evaluate each of the inverse trig functions in radians rounded to 4 decimal places

Problem 1

https://webwork.uncc.edu/webwork2_fi...0ba0ba3bb1.png

Problem2https://webwork.uncc.edu/webwork2_fi...c393e51c81.png

$\displaystyle y = \cot^{-1}(-\frac{1}{2})$

$\displaystyle \cot(y) = \frac{-1}{2}$

$\displaystyle \frac{1}{\tan(y)} = \frac{-1}{2}$

$\displaystyle \tan(y) = -2$
• Apr 5th 2009, 06:04 PM
lsnyder
i know thats wrong b/c i've typed that already.
• Apr 5th 2009, 07:12 PM
lsnyder
the amin answers i keep getting are

Problem1
-1.1071487178

Problem 2
-0.620249486

• Apr 6th 2009, 07:16 AM
stapel
Quote:

Originally Posted by lsnyder
i know thats wrong b/c i've typed that already....

the amin answers i keep getting are

Problem1: -1.1071487178

Problem 2: -0.620249486

You know what is wrong? What did you type, and where? What is an "amin" answer? How did you arrive at these values? What were your steps? What is your question?

1) By definition, arccot(-1/2) = A means cot(A) = -1/2. Then tan(A) = -2, sp arctan(-2) = A.

Plug this into your calculator, making sure the "mode" is set to "degrees" or "radians", depending upon the form required by your assignment.

2) This one works just like the previous one. (Wink)
• Apr 6th 2009, 11:17 AM
lsnyder
the homework was due last night so i got the answers now

Problem 1:
2.03445128220591

Problem 2:
2.52135051401718
• Apr 6th 2009, 02:08 PM
mr fantastic
Quote:

Originally Posted by lsnyder
the homework was due last night so i got the answers now

Problem 1:
2.03445128220591

Problem 2:
2.52135051401718

There is a subtley that needs to be addressed here:

The range of inverse tan is, by definition, approximately (-1.5708, 1.5708). BUT ..... the range of inverse cot is, by definition, approximately (0, 3.1416) (see Inverse Trigonometric Functions).

So when using the technique suggested in this thread to get inverse cot, you have to add pi (approx 3.1416) to your answer.

Alternatively (and probably more simply), you can just use the well known relationship $\displaystyle \cot^{-1} x = \frac{\pi}{2} - \tan^{-1} x$.

To the OP: You may not have got the correct answers in time for your homework but hopefully you've now learned something (which in the long run is much more important).