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/sci/ - Science & Math


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3046387 No.3046387 [Reply] [Original]

I was solving a bunch of eq. (finding x intercepts) came across one i couldnt get the answer for.
8x^2 + 21 = -59x
>8x^2 +59x +21
> 8x^2 +56x +3x +2
> 8x(x+7) (3x+2)
>(x+7) (8x+1)

which is obviously wrong. Can anyone enlighten me on how to solve for the x int. for these?

this is as far as i got

>6 (

>> No.3046399

Roots are -7 and -(1/8)

If you want more info, ill lurk on this baby for a few moments.

>> No.3046420

yea i got -8 as a root, and -1/8, however on my sheet (which is posted as correct) shows the second root as -3/8

I dont know if this step is wrong , but for some reason it seems to be right, let me explain.

::
> 8x(x+7) - now taking the first term out for the second bracket 3(x+2)

to get (x+7) (8x+3)
8x+3=0
8x=-3
=-3/8

Similarily, in this question : 15a^2-3a=3-7a

>15a^2 +9a -5a -3
>(15a^2 +9a) (-5a-3)
>3a(5a+3) -5(a-3)

roots = 5a+3 = 0 , -3/5
3a-5=0
3/5 , these values are CORRECT in both answers, so the answers cant be wrong. I think im doing something wrong in that method, and you made the same mistake, unless im wrong? englighten me

>> No.3046422

>>3046387
Why don't you just use the quadratic formula for bastards like that?

If the equation is in the form

<span class="math"> \displaystyle{ Ax^2 + Bx + C } [/spoiler]

your zeros will be

<span class="math"> \displaystyle{ \frac{ -B \pm \sqrt{B^2 - 4AC}}{2A} } [/spoiler]

>> No.3046426

ok here's what you do....get a graphing calculator go to your graph in the first y= put 8x^2+21 in the second one put -59x then zoom out and trace the intersections.....and thats algebra 2 through precal in a nutshell

>> No.3046428
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3046428

>>3046399

Me again im stupid as hell. I thought that your roots would be right. However i just did it myself and the roots are 7 and (3/8)

mfw i actually thought that i could trust your mathematical skills when you are asking for help on algebra...

>> No.3046436

(to the tune of pop goes the weasel)
X equals negative b
plus or minus the square root
of b squared minus four a c
all over 2 a!

>> No.3046442

alternatively
8x^2 + 21 = -59x
8x^2 + 59x + 21 = 0
(8x+3)(x+21) = 0
bam

>> No.3046447

>>3046442
whoops sorry that last part should say (x+7) not (x+21)

>> No.3046460
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3046460

>>3046442

>(8x+3)(x+21)

Foil that and tell me if you get
>8x^2 + 59x + 21 = 0

>mfw people who fail at basic algebra try to help other people who are struggling

>> No.3046466

im telling you just graph intersections in the calculator...you may think im trolling but its your loss so fuck this im out

>> No.3046469

>>3046460
>can't read my typo-correcting post that came three minutes before his own, buttfucker response

>> No.3046492
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3046492

>>3046469

mfw even though you did, you still made a mistake that a dolpin with downsyndrome would even make.

>> No.3046500

>>3046492

Im with this guy.

>> No.3046522

>>3046422
That formula is god mode, just learn it. It'll get you through high school and then some.

>> No.3046551

>>3046522
X EQUALS NEGATIVE B, PLUS OR MINUS SQUARE ROOT OF
B SQUARED MINUS 4 A C
ALL OVER TWO A

Dat song

>> No.3046572

>>3046492

OH U SO MAD AS FUCK CUZZ

>>3046551

DAT ALREADY POSTED ITT SONG

>> No.3047125

I'm sure the sticky has stuff on how to do this crap.

>> No.3047177

\displaystyle{ 8x^2 + 59x +21 = 0 }
\displaystyle{ x^2 +\frac {59x}{8} + \frac{21}{8} = 0 }
\displaystyle{ (x+\frac{59}{16})^2 - \frac{2809}{256} = 0 }
\displaystyle{ x = -frac{59}{16} \pm \frac{53}{16} }

testing

>> No.3047184

I'm 77
>>3047177
>>3046422
how did you do that?

>> No.3047195

>>3046422
>>3046422
>>3046422
>>3046422

HOW YOU DO THIS?!?!

>> No.3047211

>>3046422
>>3046422
>>3046422
>>3046422
>>3046422
>>3046422
>>3046422
how did you do the formula

yo I got time, I got nothing better to do, my room mate (girl) is the only one here and wont sleep with me so I got all day I'll just keep posting.

>> No.3047217

http://wwwdotmathsisfundotcom/algebra/quadratic-equation-derivation.html

>> No.3047218

>>3046422
how did you do this formula shit... I'm for serious.

>> No.3047222

>>3047211

What do you mean how do you do the formula?

>> No.3047260

He's just some dumbass who has never learned it.

<span class="math">\displaystyle a = 8, b = 59, c = 21[/spoiler]

<span class="math">\displaystyle x = \frac{-59 \pm \sqrt{59^2 - 4(8)(21)}}{2*8}[/spoiler]

<span class="math">\displaystyle x = -\frac{3}{8}[/spoiler]

<span class="math">\displaystyle x = -7[/spoiler]

>> No.3047262

><span class="math">\sqrt{x^2+1}[/spoiler]
<span class="math">\sqrt{x^2+1}[/spoiler]

>> No.3047265

I think he's asking how to write in the special math script.

>> No.3047271
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3047271

Then he can learn to stop talking like a nigger and ask just that.