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Topic: Inverse trig
Replies: 6   Last Post: May 21, 2013 11:54 AM

 Messages: [ Previous | Next ]
 Marnie Northington Posts: 1,251 Registered: 12/13/04
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

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

Date Subject Author
5/17/13 Marnie Northington
5/17/13 W. Dale Hall
5/18/13 Brian Q. Hutchings
5/20/13 Marnie Northington
5/20/13 quasi
5/20/13 quasi
5/21/13 Marnie Northington