circles

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marshall1432

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1. What is the center of the circle given by the equation (x + 5)2 + y2 = 16?

2. What is the center of the circle x2 + y2 - 8y + 1 = 0?

3. What is the equation, in general form, of the circle whose center is (1, 2) and which contains the point (1, -1)?

ok, hes what i got.

on #1 i am just stuck
on #2 i narrowed down the equation to (x2)+(y-4)=-1 or so thats what i think but after that i am stuck
on #3 i have no idea.

can anyone help me get through these? thanks
 
You certainly should these basic ideas!
\(\displaystyle \left( {x - h} \right)^2 + \left( {y - k} \right)^2 = r^2\) is the general equation for a circle.
The center is \(\displaystyle \left( {h,k} \right)\) and the radius is \(\displaystyle r\).

Using the ‘completing the square’ is the basic technique in working these problems.

For #1, the equation is in classic form. Just read off the center.

For #2, complete the square on y.

For #3, the radius is the distance from the center to any point on the circle.
 
i dont know how to do it thats the problem. you are telling me know these basic ideas. i know the formula but i dont know what to do after that.
 
For #1:
\(\displaystyle \begin{array}{rcl}
\left( {x + 5} \right)^2 + y^2 & = & 16 \\
\left[ {x - \left( { - 5} \right)} \right]^2 + \left[ {y - 0} \right]^2 & = & 4^2 \\
\end{array}.\)

Now you tell us about the center and radius!
 
so the center would be lets see, (-5,0)?
and then #2 would be (1,4) and #3 would be (x+1)2+(y+-1)2=0???
 
Yes, you did it!
Now complete the square in #2.
Tell us what you get.
 
\(\displaystyle \begin{array}{l}
\# 2\quad \Rightarrow \quad x^2 + \left( {y - 4} \right)^2 = 15 \\
\# 3\quad \Rightarrow \quad \left( {x - 1} \right)^2 + \left( {y - 2} \right)^2 = 9 \\
\end{array}\)
 
so #2 would be the center as (1,4) and #3 would stay as the equation?
please understand that i am in no way math oriented and i have a hard time learning the concepts and getting the correct answers.
 
Do you think that what you really need is good sit down with you instructor?
Why not say to her/him that you are really struggling with this?
Ask for more help!
 
i would "sit down" with my instructor but its an online class and the college is 3 hours away. i have emailed the instructor several times but havent gotten a reply.
you say you are here to help people with math and i had a question regarding math and no one could actually explain it without making me try to do steps i dont even know how to do!
 
This confirms what I have long considered to be true about online classes...NOTHING replaces a real live instructor who can respond to student questions. WE can't do that for any student...we're coming from the same place as an online class.

Please consider finding a local tutor who can help you understand this material. If you don't know where to find a tutor, contact your local community college (if you have one), or your local high school. This topic is something a high school-level tutor should be able to help with.
 
No mathematics course can be taught online!
You have been defrauded!
Now, you may have wanted an easy way out.
But, whoever is giving you this class is fooling you.
There are two possibilities:
1) You may simply need a mathematics credit. That is really an old-fashion notion. It is totally out of date. If that is the position school, the get out of there, because such an institution has no idea about modern education!
2) If your major requires that you need very basic mathematics for you major then you need a real basic mathematics course. No online course will do! Unless you are on Mars, you are close to some community college. Go there and take you mathematics courses.
 
We ARE here to help. BUT....you need to show us that you have some basic understanding of the type of problem you've asked about.

I don't see that here...you haven't shown us anything about what you have tried to do, or indicated where your specific problems are.

You are paying (I assume) for this online class...

We are volunteers....

Where should you go to get satisfaction on this course?
 
marshall1432 said:
you say you are here to help people with math and i had a question regarding math and no one could actually explain it without making me try to do steps i dont even know how to do!
Click to expand...
Unfortunately, we cannot replace the classroom instruction which you are self-evidentely not receiving. You were recommended to petition your "school" for redress because it is self-evidently not providing you with the service for which you have paid. You were recommended to hire a tutor with whom you could work face-to-face because such a tutor would be in a position to do what the volunteers at this online homework-help forum cannot: teach the missing material.

It is understandable that implications of your situation would upset you. And it is to be regretted if our inability to "fix" your situation offends you. But I'm afraid there are certain real-world practicalities in play here. We simply cannot re-teach your course, "on the side", within this environment, even were you paying the tutors for the help they've been trying to provide. Sorry.

My best wishes to you.

Eliz.
 
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