/sci/ - Science & Math » Thread #11149996

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Anonymous Fri 15 Nov 22:55:33 2019 No.11149996 View Reply Original Report

Quoted By: >>11150007 >>11150009 >>11150017 >>11150331 >>11150335 >>11150361 >>11151360

Highschool-tier you say? Sure, but can you solve it with a pencil?

Anonymous

Anonymous Fri 15 Nov 2019 22:58:02 No.11150007 Report

Quoted By:

>>11149996
by inspection, no solutions

QED

Anonymous

Anonymous Fri 15 Nov 2019 22:59:20 No.11150009 Report

Quoted By:

>>11149996
Is it a discounted cash flow equation? There must be a dedicated finance formula for that

Anonymous

Anonymous Fri 15 Nov 2019 23:00:43 No.11150017 Report

Quoted By:

>>11149996
Just rewrite the equation into a fourth-order polynomial and solve using whatever root method you like.

Anonymous

Anonymous Sat 16 Nov 2019 00:37:20 No.11150276 Report

Quoted By: >>11150301

homework thread detected

Anonymous

Anonymous Sat 16 Nov 2019 00:48:11 No.11150301 Report

Quoted By: >>11150307

>>11150276
What teacher would assign this as homework?

Anonymous

Anonymous Sat 16 Nov 2019 00:50:29 No.11150307 Report

Quoted By:

>>11150301
A middle school maths teacher.

Anonymous

Anonymous Sat 16 Nov 2019 01:01:06 No.11150331 Report

Quoted By:

>>11149996
just like

factor it out bro

and then

its a quartic at worst

bro

Anonymous

Anonymous Sat 16 Nov 2019 01:02:55 No.11150335 Report

Quoted By: >>11150343 >>11150345

>>11149996
Let x= 1+r, x=/ 0. Multiply both sides of equation by x. Get 103.75x^4=3.5x^3+3.5x^2+3.5x+103.5
Get all terms on one side, use quadratic equation to solve for x. x = 0.990993, 1.025031. r = x -1
r=-1.990993, 0.025031
Literally middle school math

Anonymous

Anonymous Sat 16 Nov 2019 01:06:07 No.11150343 Report

Quoted By:

>>11150335
It's a quartic equation

Anonymous

Anonymous Sat 16 Nov 2019 01:06:19 No.11150345 Report

Quoted By:

>>11150335
couldn't you just find the common denominator and add everything on the right and then simplify to find r?

Anonymous

Anonymous Sat 16 Nov 2019 01:11:15 No.11150355 Report

Quoted By: >>11150362 >>11152727

why is the quintic unsolvable ?

Anonymous

Anonymous Sat 16 Nov 2019 01:12:51 No.11150361 Report

Quoted By: >>11150368

>>11149996
$r=0$ is already a pretty good approximation so just do one step of Newton iteration. With $1+s=(1+r)^{-1}$ :
$103.75 = 3.5+3.5+3.5+103.5+(3.5+7+10.5+414) s + O\left(s^2\right)$
$104\approx 114+400s + O\left(s^2\right)$
$r\approx -x \approx \frac{10}{400} = .025$
I really can't be bothered to do any long division, so this is the best you'll get.
Another root can be found starting at $r=-2$ using the same procedure.

Anonymous

Anonymous Sat 16 Nov 2019 01:12:52 No.11150362 Report

Quoted By: >>11150371

>>11150355
Galois theory and all that

Anonymous

Anonymous Sat 16 Nov 2019 01:15:55 No.11150368 Report

Quoted By:

>>11150361
Should be $s$ instead of $x$ in the final line.

Anonymous

Anonymous Sat 16 Nov 2019 01:16:43 No.11150371 Report

Quoted By: >>11150385

>>11150362
what is galois theory?

Anonymous

Anonymous Sat 16 Nov 2019 01:21:10 No.11150385 Report

Quoted By: >>11150389

>>11150371
why do people ask dumbass questions when they could fucking use a search engine

Anonymous

Anonymous Sat 16 Nov 2019 01:22:28 No.11150389 Report

Quoted By: >>11151362

>>11150385
because google has shitty explanations baka

Anonymous

Anonymous Sat 16 Nov 2019 08:31:53 No.11151360 Report

Quoted By:

>>11149996
multiply both sides by (1+r)-^4, collect terms and solve for r

Anonymous

Anonymous Sat 16 Nov 2019 08:33:29 No.11151362 Report

Quoted By:

>>11150389
Use more than the first three links on the first page of the search you fucking nigger

Anonymous

Anonymous Sat 16 Nov 2019 22:02:37 No.11152727 Report

Quoted By:

>>11150355
Basically Galois considered the set of numbers that you can get by some shortlist of operations, namely addition, subtraction, multiplication, division and roots. Then he proved that a quintic can have solutions that lie outside of this set.

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