Question #07ebb

1 Answer
Aug 13, 2016

Invalid as a general formula..

Explanation:

The principal value from the calculator for arctan(y/x) in Q1

when (x, y) in Q1 or Q3 .

Likewise,

the principal value from the calculator for

arc tan (y/x) in Q2, when (x, y) in Q2 or Q4

Test with (x, y)=(+-1, +-1)

Any formula equivalent to the couple

'cos theta = x/r and sin theta = y/r', for fixing theta, is valid.

As sine and cosine are periodic with period 2pi, theta identified

in [0, 2pi] would fix the quadrant correctly.
.