SOLUTION: find the center and radius of the circle having equation x^2+y^2+2x-4y+1=0

Algebra.Com
Question 1061422: find the center and radius of the circle having equation x^2+y^2+2x-4y+1=0
Answer by Edwin McCravy(20059)   (Show Source): You can put this solution on YOUR website!


We need to get it in the form  so we'll
know it has center (h,k) and radius r.

First we add -1 to both sides to get the constant off the left side:



Next we swap the 2nd and 3rd terms to get terms with the same letter
next to each other:




Put the addition of one blank after the +2x and another after the 
-4y since we are going to add something to both sides:



Next we calculate what goes in the first blank:

1. Multiply the coefficient of x, which is 2, by }, getting 
2. Square that value:  , so  is what goes
in the first blank, and we also add it to the right side:

  

Next we calculate what goes in the second blank:

1. Multiply the coefficient of y, which is -4, by }, getting 
2. Square that value:  , so  is 
what goes in the second blank, and we also add it to the right 
side:



The first three terms on the left  factors as  
or 

The last three terms on the left  factors as  
or 

The right side  becomes 

So we now have:



And we compare that to 
 

and we see that since , , and
since , . Also  so }

So the center is (h,k) = (-1,2) and the radius = r = 2.

Edwin


RELATED QUESTIONS

given the equation of a circle x^2+y^2-10x+4y+13=0. find its center and radius. i am... (answered by Theo)
Find the center and radius of the circle... (answered by solver91311)
Find the center and radius of the circle given by the equation... (answered by stanbon)
Find the center and radius of the circle... (answered by mathman409)
If the radius of the circle x^2+y^2-6x+4y+k=0 find the equation of the circle with center (answered by ikleyn,josgarithmetic,Alan3354)
write the equation of the circle in standard form. Find the center, radius, intercepts... (answered by ewatrrr)
Find the center and radius of the circle... (answered by Fombitz,solver91311)
x^2 + y^2 - 2x + 6y - 3 = 0 (find center and radius of the... (answered by Edwin McCravy)
Complete the square and write the equation in standard form. Then give the center and... (answered by orca)