trigonometric ratios

# Angles in a circumference

To represent angles in a circumference:

- we take the O (0,0) point as vertex

- we use the radius on the positive semiaxis of abscissas as origin

- we draw the extreme of the angle by measuring it:

- counterclockwise, if it is positive

- clockwise, if it is negative

If the radius is 1, we call it goniometric circumference.

We have four quadrants:

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