Center and Radius of a circle

frichar3

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Sep 12, 2005
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I have to find the center and radius of circle 5x^2 -5x + 5y^2 + 10y +3 =0 Answer must be in decimals. :?: [/list][/list]
 
Complete the Square - Twice

5(x^2 - x + ____) + 5(y^2 + 2y + ____) +3 + _____ + _____ = 0

Fill in the blanks.
 
I did. i get to 5(x^2 - x-1/2^2) + (y^2 +2y +1^2)= -3+1/4=1 but it doesnt simplify to the right answer
 
How did you simplify? What did you get? What is the "right answer"?

Thank you.

Eliz.
 
So then ...I divide all that by 5 getting...(x^2-x+1/2^2)+(y^2+2y+1^2)=-3/5+5/4.....I think somewhere here I maek the mistake and I dont know the right answer the program just tells me I get it wrong!
Thanks all!
 
"The program"? I'm sorry, but I don't know what this means.

Meanwhile, you need to complete the squares. That means putting the stuff on the left-hand side into (x - h)<sup>2</sup> and (y - k)<sup>2</sup> form, so you can read off the center (h, k) from the equation. Also, you need to simplify the values on the right-hand side. You have two numbers; add them.

Eliz.
 
My class does its homework on webwork....I do all that and get
(x-1/2)^2+(y+1)^2=.65 meaning h,k is -1/2,1 and the radius is .65 but it says incorrect.
 
tkhunny said:
Complete the Square - Twice

5(x^2 - x + ____) + 5(y^2 + 2y + ____) +3 + _____ + _____ = 0

Fill in the blanks.
Let's try that again, from here.

You have correctly, (1/2)<sup>2</sup> and 1<sup>2</sup>. Your notation does not say that. -1/2<sup>2</sup> is not the same as (-1/2)<sup>2</sup>. You need to decide what you mean and make sure that is what you write.

You also overlooked the constants that were factored out. See those 5s? You can't skip them. The values you add INSIDE the parentheses are multiplied by those constants. This gives:

5(x^2 - x + (1/2)<sup>2</sup>) + 5(y^2 + 2y + 1<sup>2</sup>) +3 - 5*(1/2)<sup>2</sup> - 5*1<sup>2</sup> = 0

It seems I faked you out a little by putting addition in front of the blanks at the end. You must add or subtract as necessary so that the value of the expression is not changed.

Now, let's see what you can do with it.
 
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