# Problem 13: Polar Derivatives

## 2011-2012

Find all angles on the interval  at which the tangent line to the graph of the polar equation  is horizontal.

### Solution:

Express the polar equations parametrically (in terms ofx and y) and calculate the slope of the polar equation.

The tangent lines to the polar graph are horizontal when the numerator of this derivative is equal to 0. In other words, at .

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