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Find the sum of all possible values of the constant  such that the graph of the parametric equations
\(\begin{align*} x &= 2+ 4\cos s,\\ y &= k-4\sin s, \end{align*}\)
intersects the graph of the parametric equations
\(\begin{align*} x&=1+\cos t,\\ y&=-3+\sin t \end{align*}\)
at only one point.

 Nov 28, 2018

Best Answer 

 #1
avatar+3958 
+2

We need to use trickery here.

 

The first set of equations is a circle of radius 4 centered at (2,k)

The second set is a circle of radius 1 centered at (1,-3)

 

A grazing solution will be such that the distance between their centers will be equal to the sum of their radii.

 

\(\text{we'll use the distance squared}\\ (2-1)^2+(k+3)^2 = (1+4)^2 = 25\\ 1+k^2+6k+9=25\\ k^2+6k-15=0\\ k=\dfrac{-6\pm\sqrt{36+60}}{2}\\ k = -3\pm 2\sqrt{6}\)

.
 Nov 28, 2018
 #1
avatar+3958 
+2
Best Answer

We need to use trickery here.

 

The first set of equations is a circle of radius 4 centered at (2,k)

The second set is a circle of radius 1 centered at (1,-3)

 

A grazing solution will be such that the distance between their centers will be equal to the sum of their radii.

 

\(\text{we'll use the distance squared}\\ (2-1)^2+(k+3)^2 = (1+4)^2 = 25\\ 1+k^2+6k+9=25\\ k^2+6k-15=0\\ k=\dfrac{-6\pm\sqrt{36+60}}{2}\\ k = -3\pm 2\sqrt{6}\)

Rom Nov 28, 2018

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