Cos(135°) = -√2/2
Cosine — the x-coordinate of the corresponding unit-circle point, or adjacent/hypotenuse in a right triangle.
How to derive cos(135°)
135° is in quadrant II. Reference angle = 45°, cosine negative in Q2, so cos(135°) = −cos(45°) = −√2/2.
Unit-circle context
The angle 135° corresponds to 3π/4 radians and sits Quadrant II on the unit circle.
Its reference angle is 45°, which is why cos(135°) shares its absolute value with cos(45°).
Other trig values at 135°
Related cos values
Frequently asked
- What is the exact value of cos(135°)?
- The exact value is -√2/2. Its decimal approximation is -0.70711.
- How do you derive cos(135°)?
- 135° is in quadrant II. Reference angle = 45°, cosine negative in Q2, so cos(135°) = −cos(45°) = −√2/2.
- What is 135° in radians?
- 135° equals 3π/4 radians (multiply degrees by π/180).
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