SOLUTION: please solve this problem: For what value of k will the equation below describe a circle of radius 3 units? x^2 + Y^2 + 2X - 4Y + K = 0

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Question 321940: please solve this problem:
For what value of k will the equation below describe a circle of radius 3 units?

x^2 + Y^2 + 2X - 4Y + K = 0
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Complete the square in x and y.
x%5E2+%2B+y%5E2+%2B+2x+-4y+%2B+K+=+0
x%5E2%2B+2x++%2B+y%5E2-4y+%2B+K+=+0
%28x%5E2%2B+2x%2B1%29++%2B+%28y%5E2-4y%2B4%29+%2B+K+=+1%2B4
%28x%2B1%29%5E2%2B%28y-2%29%5E2=5-K
Compare to the general equation of a circle centered at (h,k) with a radius R.
%28x-h%29%5E2%2B%28y-k%29%5E2=R%5E2
R%5E2=5-K=9
highlight%28K=-4%29