Need help with a college algebra problem

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romanianxromo

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Apr 2, 2008
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The question is:

Identify the center and radius of the circles represented by the following questions

(a) 12x² + 12y²+42y=0

Do you divide first by 6 then you get 2x²+2y²+7y=0 ? If so, I'm confused as to what I should do after that

Thank you!
 
Divide by 2 and get those quadratic terms clean.

x² + y² + (3/2)y = 0

Then, Completing the Square on the y's is the way to go. Do you remember how to do that?

x² + y² + (3/2)y + ____ = 0 + ____

(3/2)/2 = 3/4

(3/4)² = 9/16

x² + y² + (3/2)y + 9/16 = 0 + 9/16

x² + [y + (3/4)]² = (3/4)²

Ringing any bells?
 
Yes, all the way until the last step.

How do I find my x and y value for the center? and is the radius just (3/4)2? which would be 9/16?
 
romanianxromo said:
Yes, all the way until the last step.

How do I find my x and y value for the center? and is the radius just (3/4)2? which would be 9/16?
Click to expand...

equation of a circle is:

\(\displaystyle (x-h)^2 + (y-k)^2 = r^2\)

where the coordinate of the center is (h,k) and the radius is 'r'.

Compare the above with the last equation tkhunny derived for you.
 
I'm sorry but math is the one thing I cannot understand.

I'm not sure what to do past the x^2 + [y+(3/4)]^2 = (3/4)^2

The radius is just (3/4)^2 which is 9/16, correct?

But with the formula you just gave me, I'm having trouble finding the h and k
 
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