[H]excel

Steelflight-Rx

United States1389 Posts

October 15 2008 22:52 GMT

Does anyone know if there's a way to solve quadratics using excel? (other than manually typing in the formula). Excel help is totally useless =S

EtherealDeath

United States8366 Posts

October 15 2008 22:54 GMT

http://phoenix.phys.clemson.edu/tutorials/excel/algebra.html

Google is the closest thing to God man has ever created. Remember this young padawan, when your prayers are not answered in time.

micronesia

United States24753 Posts

October 15 2008 22:56 GMT

Why are you using excel to solve quadratics? Doing a project in excel where you just happen to need to solve a quadratic?

edit: yeah that tutorial just says to manually type in the quadratic formula by using the cells of a b and c.

edit2: if you can come up with a reason why that method isn't good, please explain why

Steelflight-Rx

United States1389 Posts

October 15 2008 23:17 GMT

i used google and came up with that result. The only problem is that the result using that method disagrees with the answer given in the book by 0.0006, which is pretty significant when the answer in question is 0.0068 vs 0.0062.

So in response to edit2: The prescribed method is not accurate enough to give me a reasonable answer when compared with the answer in the book. I guess that really doesn't answer the question why, which is probably something to do with the way excel does its math, which is why I was wondering if there was a function that did the calculations by some predetermined algorithm with a higher level of accuracy.

Steelflight-Rx

United States1389 Posts

October 15 2008 23:18 GMT

but thanks micronesia, dont wanna seem like a douche, i appreciate the effort

just the way you posed the question made me feel like answering it in essay form lol

GHOSTCLAW

United States17042 Posts

October 15 2008 23:47 GMT

It sounds like you're running into the problem of excel clipping the numbers. you need to change the precision in excel to a "long" type number format, or figure out how to get the decimals more precise.

Raithed

China7078 Posts

October 15 2008 23:56 GMT

just plug it in.

Steelflight-Rx

United States1389 Posts

October 15 2008 23:57 GMT

On October 16 2008 08:56 Raithed wrote:
just plug it in.

.. thats what i did but im losing precision somewhere, my answer is off by +0.0006, which is too much for the calculations i'm doing.

lol srsly man theres only like 4 posts in this blog, you couldn't read them?

Nitrogen

United States5345 Posts

October 16 2008 00:14 GMT

right click -> format cells -> decimal places?

not sure if this is what you mean, but you can just add on a bunch of decimal places for more precision

edit: i think you have to select all cells before you do this if you want them all to have a bunch of decimal places.

JeeJee

Canada5652 Posts

October 16 2008 00:14 GMT

#10

off the top of my head, your problem could be that excel is solving it iteratively up to a certain # of calculations, which you can change to add arbitrarily good precision. i haven't looked at any links or have any idea how you're solving the equation, but you can give this a try.
i highly doubt it's a rounding error but you can look at that as well

MasterOfChaos

Germany2896 Posts

October 16 2008 10:29 GMT

#11

for b>>ac the one of the results is typically i inexact because you are subtracting similar sized numbers which leads to rounding errors with floats.
So calculate:

$[image loading]$

(for x^2+px+q=0 so p=b/a q=c/a)
which is a wellknown trick to reduce the rounding errors.
But no idea if that works with excel, I don't use it very often.

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