Join TSR now and get all your revision questions answeredSign up now

Trig Watch

    • Thread Starter


    For alpha I did inverseTAN (-2/-5) and got 0.38 radians says the answer is -2.76 I don't know how?
    • Very Important Poster

    (Original post by khanpatel321)

    For alpha I did inverseTAN (-2/-5) and got 0.38 radians says the answer is -2.76 I don't know how?
    If you go back and say that Rsinalpha * sinx = -2 then you will see why 0.38 doesn't work but -2.76 works.

    Notice that -2.76 looks suspiciously like 0.38 - pi (3.1415926...)

    This ambiguity between quadrants is a feature of the arctan function. If, as in this case, you have both the y and x components of the arctan, you should always look at the respective signs to see what quadrant the angle must be in. With the y and x components both negative, the angle must be in the third quadrant. That means that even if your calculator's arctan function returns a result of 0.38, the actual angle must be pi+0.38 or -(pi-0.38). These two forms of the answer are 2pi apart, and are therefore equivalent.
Is GoT overrated?
Useful resources

Make your revision easier


Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here


How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.