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**Soroban** Hello, Egoist!

The center of the circle is: .$\displaystyle C(1280,800)$

The radius is: .$\displaystyle r \:=\:650$

Suppose the two given points are: .$\displaystyle P(x_1,y_1),\;Q(x_2,y_2)$

Find the slope of $\displaystyle CP\!:\;\;m_1 \:=\:\frac{y_1-800}{x_1-1280}$

Find the slope of $\displaystyle CQ\!:\;\;m_2 \:=\:\frac{y_2-800}{x_2-1280}$

The angle $\displaystyle \theta$ between the two radii is given by: .$\displaystyle \tan\theta \:=\:\frac{m_2-m_1}{1 + m_1m_2}$

. . Find $\displaystyle \theta$ in *radians*.

The arc length between $\displaystyle P$ and $\displaystyle Q$ is: .$\displaystyle s \;=\;r\theta$