Question 66

Find the value of $$\cos225^{\circ}$$

Solution

$$\cos225^{\circ}$$ = $$\cos\left(180+45^{\circ}\right)$$

= $$-\cos45^{\circ\ }$$

= $$-\frac{1}{\sqrt{2}}\ $$

= $$-\frac{1}{\sqrt{2}}\ \times\frac{\sqrt{2}}{\sqrt{2}}$$

= $$-\frac{\sqrt{2}}{2}\ $$

= $$-\frac{1.4142}{2}\ $$

= $$-0.7071\ $$

Hence, the correct answer is Option D

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