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**Prove It** You should know that $\displaystyle \displaystyle x= r\cos{\theta}$ and $\displaystyle \displaystyle y = r\sin{\theta}$, where $\displaystyle \displaystyle r$ is the radius (in your case, length of the arm).

So first evaluate $\displaystyle \displaystyle r$ using Pythagoras and your two points $\displaystyle \displaystyle (0,0)$ and $\displaystyle \displaystyle (20,21)$, then you can evaluate $\displaystyle \displaystyle \sin{\theta}$ and $\displaystyle \displaystyle \cos{\theta}$.

Do the same for Q7.