November 25, 2015

Homework Help: trigonometry

Posted by michelle on Tuesday, May 1, 2007 at 8:27pm.

How do you find: cot(-5pie/4)?

you have to know that cotx = 1/tanx

so you could just trustfully change your calculator to radians
enter 5*pi/4, press =, press +/-,
then press Tan, =, then the 1/x key
you should get -1


you could do it the more rewarding way without a calculator.

pi/4 radians is 45, so 5pi/4 is 225
-225 is a clockwise rotation and lands you in the second quadrant where the tan is negative, and 45 up from the x-axis.
now tan45=1, so tan(-225)=-1
then cot(-225)=1/-1=-1


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