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kjones
06-01-2006, 09:24 AM
Solve using quadratic formula:

4x^2 + 8x - 16 = 0

stapel
06-01-2006, 09:30 AM
So plug the numbers they gave you into the formula you've memorized, and chug away to the answer.

Where are you stuck? Please reply with details.

Thank you.

Eliz.

kjones
06-01-2006, 09:55 AM
When I figured 8^2 - 4(4)(-16) I was getting -256. I have to change the sign? K

Denis
06-01-2006, 10:08 AM
Kaye, steveb showed you how to solve these; what do you not understand?

Start by dividing each term by 4

And - 4(4)(-16) = 256, NOT -256

kjones
06-01-2006, 10:17 AM
Dennis,

The numbers plugged into the quadratic formula should be simple, but, not for me it seems.

The square root of 8 is 64 and there is a (-) sign in between that and the 256. That is why I was getting 64 - 256 = -192 instead of the 320.

I'm not sure about dividing both sides by 4.

Can one get booted from this excellent service or being so dense?

K

Mrspi
06-01-2006, 10:50 AM
Solve using quadratic formula:

4x^2 + 8x - 16 = 0

Whether you are going to solve a quadratic equation by factoring, completing the square, or by the quadratic formula, smaller numbers are generally easier to work with than larger numbers.

Note that each term in your equation is evenly divisible by 4. So, let's divide both sides of the equation by 4:

x<sup>2</sup> + 2x - 4 = 0

Now, you can use the quadratic formula with
a = 1, b = 2, and c = -4

Substitute these values into the formula:

x = [-2 +/- √(2<sup>2</sup> - 4(1)(-4))] / 2(1)

BE VERY CAREFUL when doing the computation of the quantity under the radical sign. That is where most mistakes occur when using the quadratic formula. I'll walk you through it in baby steps:
(2<sup>2</sup> - 4(1)(-4))
Remember the order of operations. Do the power first:
(4 - 4(1)(-4))
Next, do the multiplications:
(4 - (-16))
Finally, do the subtraction. Remember that 4 - (-16) is the same thing as 4 + 16:
4 + 16
20
So, the expression under the radical sign is 20, and we continue:

x = [-2 +/- √20 ] / 2
We can simplify √20......it is 2 √5. Now we have this:

x = [-2 +/- 2 √5] / 2

or,
x = 2[-1 +/- √5] / 2
or,
x = -1 +/- √5

kjones
06-01-2006, 08:56 PM
Your explanation is very helpful. I appreciate your guidance. I'll keep these instructions to prepare myself for the final. Just finished the mid-term tonight. I'm taking a 5-week summer session in college and it is very intense. This helps me very much.
K