standard_description: Know the formulas for the area and circumference of a circle and use them to solve problems; give an informal derivation of the relationship between the circumference and area of a circle.
problem_activity: Task
Consider a circle with center $O$ and let $P\,$ be a point on the circle. Suppose $L$ is a tangent line to the circle at $P$,  that is $L$  meets the circle only at $P$.
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Show that $\overline{OP}\,$ is perpendicular to $L$.


aligns: no