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Inverse trig
Posted:
May 17, 2013 2:31 PM


I was assisting a student with finding all the answers to such questions as sin x = 1/2 in the usual four quadrants from 0 to 360.
The student had been told not to use a calculator, which I thought was an excellent idea, but I couldn't resist using a calculator myself just to see which quadrant it used for the answer.
This led to the question of why does the calculator not use the usual four quadrants for its inverse trig functions?
Clearly these functions require a range of 1 to +1 for inverse sin and cos and lots to +lots for inverse tan.
It seems to me that any three adjacent quadrants will satisfy this requirement.
For inverse tan, the calculator is clearly using the range 90 to +90 which includes what might be called the zeroth quadrant.
For inverse sin and cos it's using the range 90 to +180
Have I missed the good reason for this?
Old guy



