Confused

C

christina18

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Apr 3, 2006
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can somebody please tell me how to solve this problem, i know i most likely have to use the quadratic formula but it's confusing me.

Solve by completing the square: x^2-8x-4=0
 
The exercise says that you are to solve by completing the square, not to solve by applying the Quadratic Formula. So I would suggest using the completing-the-square process to solve.

Eliz.
 
Completing the square process means factoring first? and then setting up each part to zero then solve?
 
No, "Completing the Square" is "Completing the Square". Have you never heard of it?

Use this property.

(a+b)^2 = a^2 + 2ab + b^2

So,

x^2 - 8x - 4 = 0
x^2 - 8x = 4
x^2 - 8x + ______ = 4 + ______

Fill in the blanks. They are the same.
 
christina18 said:
x^2 - 8x + _4_____ = 4 + __8x____
Click to expand...
Why would you add "4" to one side of the equation but "8x" to the other side, thus changing the equation?

You didn't answer to tutor's question, but it would seem, from what you've posted, that somehow you missed the class meetings that covered "solving quadratics by completing the square". Here are some online lessons which may serve to substitute for those missed classes:

. . . . .Paul's Online Math Notes: Quadratic Equations, Part II

. . . . .Ask Dr. Math: Completing the Square

. . . . .The Math Page: Completing the Square

. . . . .Ask Dr. Math: How Does Completing the Square Work?

. . . . .Ask Dr. Math: Completing the Square Using a Diagram

. . . . .Completing the Square: Solving Quadratics

Once you have studied some or all of these lessons and have learned the basic technique, please re-attempt this exercise. If you get stuck, please reply showing all of your steps.

Thank you.

Eliz.
 
christina18 said:
x^2 - 8x + _4_____ = 4 + __8x____
Click to expand...
You're just guessing. Please see the references provided. There should be a section in your book, as well.
 
christina18 said:
x^2-8x-4=0
Click to expand...
to complete the square you must create a "perfect" square to do so move the 4 the the other side
\(\displaystyle x^2-8x=4\)

to complete the square you take half of b and square it
b=-8 in this case
-8/2=-4^2=16

so you add 16 to both sides
\(\displaystyle x^2-8x+16=20\)
then you because you know that it is a perfect square you know that
x^2-8x+16=(x-4)^2 so
\(\displaystyle (x-4)^2=20\)
that is how you complete the square do you understand?
 
I didn't solve the whole problem, I just completed the square. I thought the best way to teach this person how to complete the square was by showing as this is how I learn best, I thought the hints given by others were not enough.(note:i didn't look at the websites) Sometimes you need an example worked out for you :)
 
kaebun said:
I didn't solve the whole problem, I just completed the square. I thought the best way to teach this person how to complete the square was by showing as this is how I learn best, I thought the hints given by others were not enough.(note:i didn't look at the websites) Sometimes you need an example worked out for you :)
Click to expand...

I agree....you did just fine in your explanation. And I find nothing wrong with working one problem all the way through. A complete example is sometimes all a student needs to be able to complete his/her assignment.
 
... except when the student has shown no ability whatsoever to solve the problem as stated. There is clearly a background probelm, here. The student needs the background.
 
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