Question 34074
To express ctn -249 degrees as the same function of a positive acute angle, you first need to find a reference angle.  Also, it will be easier to convert to a positive angle so we'll add 360 degrees as well. The trig functions repeat themselves- they are periodic. So, draw a rough sketch of the ange on the coordinate plane and find out which quadrant you are in. Remember that quadrant I is on the upper right and it goes counterclockwise. Here are the rules for finding a reference angle: 
Quadrant II: (91-179 degrees) Use the formula 180 - a.
Quadrant III: (181-269 degrees)Use the formula a - 180.
Quadrant IV:(271-359 degrees)Use the formula 360 - a.
Another thing to remember for trig functions are the signs. All six functions are positive in QI, Sine and Cosecant are positive in Q II, Tan and Cotangent are positive in QIII, while Cosine and Secant are positive in Quad IV. I know that’s a mouthful! But, if your angle falls in a quadrant that is negative for your function, you must add a negative sign. In this case, cosine is negative in the second quadrant so our answer will have a negative sign. 

So, in your case, you want ctn -249 degrees. First convert to a positive angle by adding 360 and then sketch ctn111 degrees. From our sketch, we would be in Quadrant 2. So, use 180 - 111 = 69. Cot is negative in the 2nd quadrant so we need a negative sign also.  
-cot 69 degrees