• May 20th 2010, 08:31 AM
I entered a new era of erm...unhappiness when it comes to this...Could someone help with these...

Using the quadratic formula to solve x2 – 4 = 0 and -4x2 + 4x + 80 = 0

This keeps getting harder lol I know how to do the simple ones but when they are switched up like that it gets hard...
• May 20th 2010, 08:35 AM
harish21
Quote:

Originally Posted by tysonrss
I entered a new era of erm...unhappiness when it comes to this...Could someone help with these...

Using the quadratic formula to solve x2 – 4 = 0 and -4x2 + 4x + 80 = 0

This keeps getting harder lol I know how to do the simple ones but when they are switched up like that it gets hard...

$\displaystyle x^2 - 4 = 0$

$\displaystyle x^2 - (2)^2 = 0$

since $\displaystyle a^2 - b^2 = (a+b)(a-b)$

you can write $\displaystyle (x+2)(x-2) = 0$ and find x.

for $\displaystyle -4x^2+4x+80=0$ use the quadratic equation formula.

For a quadratic equation $\displaystyle ax^2+bx+c=0$, you can find x as:

$\displaystyle x = \frac{-b \pm \sqrt{b^{2}-4ac}}{2a}$

use a, b, and c from your equation to find x.
• May 20th 2010, 08:43 AM
Quote:

Originally Posted by harish21
$\displaystyle x^2 - 4 = 0$

$\displaystyle x^2 - (2)^2 = 0$

since $\displaystyle a^2 - b^2 = (a+b)(a-b)$

you can write $\displaystyle (x+2)(x-2) = 0$ and find x.

for $\displaystyle -4x^2+4x+80=0$ use the quadratic equation formula.

For a quadratic equation $\displaystyle ax^2+bx+c=0$, you can find x as:

$\displaystyle x = \frac{-b \pm \sqrt{b^{2}-4ac}}{2a}$

use a, b, and c from your equation to find x.

It seems (x = -5) (x = 10) could be appropiate right?
• May 20th 2010, 09:03 AM
harish21
Quote:

Originally Posted by tysonrss
It seems (x = -5) (x = 10) could be appropiate right?

Looks like you have not seen that formula before.. What method does your book or your class instructor follow to solve these type of questions?
• May 20th 2010, 09:10 AM
Quote:

Originally Posted by harish21
Looks like you have not seen that formula before.. What method does your book or your class instructor follow to solve these type of questions?

Actually it's online, and the lesson has that formula but the answers are a bit different, the one you solved for me was

x = -2 or x = 2 as an anser for my class, I could tell the difference between your anser in mine, though they looked different I think it's the same either way.
• May 20th 2010, 09:17 AM
harish21
Quote:

Originally Posted by tysonrss
Actually it's online, and the lesson has that formula but the answers are a bit different, the one you solved for me was

x = -2 or x = 2 as an anser for my class, I could tell the difference between your anser in mine, though they looked different I think it's the same either way.

(x+2)(x-2)=0 means that x = 2 or x = -2 is your answer..

I was talking about the second problem.. Are you supposed to use the formula I gave earlier on, or are you supposed to do it by completing the square?
• May 20th 2010, 09:22 AM
Quote:

Originally Posted by harish21
(x+2)(x-2)=0 means that x = 2 or x = -2 is your answer..

I was talking about the second problem.. Are you supposed to use the formula I gave earlier on, or are you supposed to do it by completing the square?

Oh, it says use the quadratic formula but I got the anwser
x = -5 or x = 10
• May 20th 2010, 09:27 AM
harish21
Quote:

Originally Posted by tysonrss
Oh, it says use the quadratic formula but I got the anwser
x = -5 or x = 10

If your question is $\displaystyle -4x^2+4x+80=0$, then the answer you have gotten is wrong...

plug in a= -4 , b = 4 and c =80 in the formula given in Post#2 and find x..
• May 20th 2010, 09:30 AM
Quote:

Originally Posted by harish21
If your question is $\displaystyle -4x^2+4x+80=0$, then the answer you have gotten is wrong...

plug in a= -4 , b = 4 and c =80 in the formula given in Post#2 and find x..

x = 5 or x = -4?
• May 20th 2010, 09:36 AM
harish21
Quote:

Originally Posted by tysonrss
x = 5 or x = -4?

correct!
• May 20th 2010, 09:40 AM
Quote:

Originally Posted by harish21
correct!

lol seriesoulsy? because I guessed lol
• May 20th 2010, 09:44 AM
harish21
Quote:

Originally Posted by tysonrss
lol seriesoulsy? because I guessed lol

Well, thats gonna harm you, not me, in the exam..