Answers

2014-01-12T20:55:14+08:00
Given:
center of circle: (-4,2)
y=2(\frac{4}{5})+2

Solution:
Using the point slope equation and the fact that perpendicular lines are negative reciprocals of each other. 

y - 2 = (-1/2)(x+4)
2y - 4 = -x - 4
2y = -x
y = \frac{-x}{2}

Since the equation above is the equation of the line perpendicular to y=2x+2, we can find the point of intersection

2x + 2=\frac{-x}{2}
4x + 4 = -x 
4x + x = -4
x = \frac{-4}{5}

Subtstituting x in the give equation you get,
y=2(\frac{-4}{5})+2
x = \frac{2}{5}

Using the distance formula you get the radius of the circle.
r =  \sqrt{(x_{2}-x_{1})^2+(y_{2} - y_{1})^2 }


0
r = 8/square root of 5
the equation is (x+4)^2 + (y-2)^2 = 64/5