10.3 day 2 Calculus of Polar Curves Greg Kelly, Hanford High School, Richland, WashingtonPhoto by Vickie Kelly, 2007 Lady Bird Johnson Grove, Redwood National Park, California
Try graphing this on the TI-84.
Polar-Rectangular Conversion Formulas
To find the slope of a polar curve: We use the product rule here.
To find the slope of a polar curve:
Example:
Find the slope of the curve at the given values. Find the points where the curve has horizonal or vertical tangent lines.
The length of an arc (in a circle) is given by r. when is given in radians. Area Inside a Polar Graph: For a very small , the curve could be approximated by a straight line and the area could be found using the triangle formula:
We can use this to find the area inside a polar graph.
Example: Find the area enclosed by:
Notes: To find the area between curves, subtract: Just like finding the areas between Cartesian curves, establish limits of integration where the curves cross.
Find the area of the region that lies inside the circle r = 3 and outside the cardioid.
When finding area, negative values of r cancel out: Area of one leaf times 4:Area of four leaves:
Find the area that lies outside the four-petal rose and inside the circle.
To find the length of a curve: Remember: For polar graphs: If we find derivatives and plug them into the formula, we (eventually) get: So:
Or… Convert to Parametric! Find the length of the cardioid
There is also a surface area equation similar to the others we are already familiar with: When rotated about the x-axis: