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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