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

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Marnie Northington

Posts: 1,251
Registered: 12/13/04
Inverse trig
Posted: May 17, 2013 2:31 PM
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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

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

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