find cos(-135 degrees)

Answer 1

cos (-135)°

cos (135°)

(cos 90° + 45°)

[cos 90° cos 45° - sin 90° sin 45°]

[0 - sin 45°]

-sin 45°

-√2 / 2

Answer 2

We know that -135 degrees (going clockwise) is the same as 225 degrees (going counterclockwise). This lies in the 3rd quadrant. Taking the nearest x-axis, we find the reference angle to be 45 degrees. Either by going back to the special triangle (45-45-90 triangle) or finding cos(45 degrees) in the first quadrant, we get that cos(45 degrees) is sqrt2/2. We also know that cosine in the third quadrant is negative, thus our final answer is -sqrt2/2.

Answer 3

1. coterminal angle of -135 degrees is +225 degrees
2. reflexive angle= 45 degrees
3. cos(45)= sqrt(2)/2 however 225 degrees is in the III quadrant and cos in the III quadrant is negative
4. answer: - sqrt(2)/2
5. or you can plug into calculator if you want an approximation