Sine Values by Quadrant
The unit circle is divided into four quadrants. The sign of sine depends on which quadrant the angle falls in. Sine is positive in Quadrants I and II (where y-coordinates are positive) and negative in Quadrants III and IV.
Quadrant Reference
Quadrant I (0° - 90°)
All trig functions are positive.
sin(+), cos(+), tan(+)
Quadrant II (90° - 180°)
Only sine is positive.
sin(+), cos(-), tan(-)
Quadrant III (180° - 270°)
Only tangent is positive.
sin(-), cos(-), tan(+)
Quadrant IV (270° - 360°)
Only cosine is positive.
sin(-), cos(+), tan(-)
Common Sine Values in Degrees
- sin(0°) = 0
- sin(30°) = 1/2 = 0.5
- sin(45°) = √2/2 ≈ 0.7071
- sin(60°) = √3/2 ≈ 0.8660
- sin(90°) = 1
- sin(120°) = √3/2 ≈ 0.8660
- sin(135°) = √2/2 ≈ 0.7071
- sin(150°) = 1/2 = 0.5
- sin(180°) = 0
- sin(270°) = -1
- sin(360°) = 0
What is a Reference Angle?
The reference angle is the acute angle formed between the terminal side of the given angle and the x-axis. It is always between 0° and 90°. The sine of any angle equals the sine of its reference angle (with appropriate sign based on quadrant).