Trigonometry uses a cast diagram to show the relationship between angles and trigonometric functions in the four quadrants. The first quadrant has all positive trigonometric functions (sine, tangent, cosine) when the angle is between 0 and 90 degrees. The other three quadrants have different combinations of positive and negative trigonometric functions depending on whether the x-value is positive or negative, and whether the y-value is positive or negative.

1. Trigonometry
The cast diagram
1st Quadrant
S A
T C
+ +
+ +
All
positive
Sin
positive
Tan
positive
Cos
positive
4th Quadrant
3rd Quadrant
2nd Quadrant 1st Quadrant
4th Quadrant
3rd Quadrant
2nd Quadrant
C
A
S
T