Question 35

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Jambmaths question: 

If angle θ is 135o, evaluate cos θ

Option A: 

$\frac{1}{2}$

Option B: 

$\tfrac{\sqrt{2}}{2}$

Option C: 

$\tfrac{-\sqrt{2}}{2}$

Option D: 

$-\frac{1}{2}$

Jamb Maths Solution: 

$\begin{align}  & \cos {{135}^{0}}=\cos ({{180}^{0}}-{{45}^{o}}) \\ & \cos {{135}^{0}}=-\cos {{45}^{o}}\text{   (cosine is -ve in the 2nd quadrant)} \\ & \cos {{135}^{0}}=-\frac{1}{\sqrt{2}}=-\frac{1}{\sqrt{2}}\times \frac{\sqrt{2}}{\sqrt{2}} \\ & \cos {{135}^{0}}=-\frac{\sqrt{2}}{2} \end{align}$

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