Consider the polar curve defined below.r = 9a sin(๐)(a) Find the points of horizontal tangency to the polar curve. (Use pi for ๐ as necessary.)( โ9a , 3ฯ2โ ) (smaller r value)( 9a , ฯ2โ ) (larger r value)(b) Find the points of vertical tangency to the polar curve.( , ) (smaller ๐ value)( , ) (larger ๐ value)
Question
Consider the polar curve defined below.r = 9a sin(๐)(a) Find the points of horizontal tangency to the polar curve. (Use pi for ๐ as necessary.)( โ9a , 3ฯ2โ ) (smaller r value)( 9a , ฯ2โ ) (larger r value)(b) Find the points of vertical tangency to the polar curve.( , ) (smaller ๐ value)( , ) (larger ๐ value)
Solution
(a) The points of horizontal tangency to the polar curve occur when the derivative of r with respect to ๐ is zero.
The derivative of r = 9a sin(๐) with respect to ๐ is dr/d๐ = 9a cos(๐).
Setting this equal to zero gives cos(๐) = 0, which has solutions ๐ = ฯ/2 and ๐ = 3ฯ/2.
Substituting these values back into the equation for r gives r = 9a sin(ฯ/2) = 9a and r = 9a sin(3ฯ/2) = -9a.
So the points of horizontal tangency are (9a, ฯ/2) and (-9a, 3ฯ/2).
(b) The points of vertical tangency to the polar curve occur when the derivative of r with respect to ๐ is undefined.
The derivative dr/d๐ = 9a cos(๐) is undefined when cos(๐) is not defined, which never happens for real values of ๐.
Therefore, there are no points of vertical tangency to the polar curve.
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