Explanation:
(i)cos(225°) = -cos(45°) = = -√(2)/2 ≈-0.707
How this answer came?
So we applied a method: Reference angle method,
so that we could find the trigonometry values, which's -cos(45°)
However,the question arises: Why it's negative?
We made it negative because cos (45°) is a third quadrant in trig, so it's always negative.
The answer could be shown in decimal form as well:
≈-0.707
(ii)sin(225°) = -sin(45°) = -√(2)/2 ≈ 0.707
How this answer came?
Well, this is same process as cos: applying reference method, changing the sign from positive to negative, could be shown in decimal as well.
Hope this helps! ^^"