If angle \(\theta\) is 135°, evaluate cos\(\theta\)
\(\frac{1}{2}\)
\(\frac{\sqrt{2}}{2}\)
\(-\frac{\sqrt{2}}{2}\)
\(-\frac{1}{2}\)
Correct answer is C
\(\theta\) = 135°
Cos 135° = Cos(90 + 45)°
= cos90° cos45° - sin90° sin45°
= 0cos45° - (1 x \(\frac{\sqrt{2}}{2}\))
= \(-\frac{\sqrt{2}}{2}\)