# i need algebra help!

Discussion in 'The Okie Corral' started by cowboywannabe, Apr 6, 2012.

1. ### cowboywannabeyou savvy?

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where can i find an on-line site that will let me put in things like: 3/4 cubed(3) - 3/10 squared + 1 1/2 cubed - 7/8 cubed = ?

2. ### cgwahlSheriffs a near

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Last edited: Apr 6, 2012

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4. ### KhufuPharaoh

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Calculators do it too....there is one included with Windows free of charge. After you open the calculator go to "view" and check teh "scientific" radio box (or when in calculator use Alt+2 and it opens scientific).

-Dana

5. ### cowboywannabeyou savvy?

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thanks, i used the google one and it gave me the answer in a decimal form, but i need the fractional form like a 5 2/3^2 or something.

6. ### cowboywannabeyou savvy?

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here is the problem:

(7/10^3 - 3/8^ - 1/5) - (-1/10^3 + 3/8^ - 1/5) = -9.59400 according to google. but i need to: change the signs of the second polynomial and collect like terms. answer is: 4/5^3 - 3/4^

this is the type of calculating i need. and the ^2 sign is suppose to be the "x square" right?

Last edited: Apr 6, 2012
7. ### J_GAFAR

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Why do you need a calculator for this? Are you trying to check a whole bunch of answers very quickly?

ETA: And you shouldn't, for example, write 8^ to mean "8 squared". Write the exponent out, i.e. write 8^2

Last edited: Apr 6, 2012
8. ### cgwahlSheriffs a near

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You're probably out of luck in regards to a calculator that will maintain fractions. But, what you could possibly do is substitute the fraction for an x and y and calculate it that way.

For instance, using your example above:

(7/10^3 - 3/8^2 - 1/5) - (-1/10^3 + 3/8^2 - 1/5) =

x = 1/10
y = 1/8

This would go into the caluclator: (7x^3 - 3y^2 - 1) - (-x^3 + 3y^2 - 1) =

7x^3 - 3y^2 -1 + x^3 - 3y^2 + 1 =
8x^3 - 6y^2 =
(8/10)^3 - (6/8)^2 =

(4/5)^3 - (3/4)^2

9. ### KhufuPharaoh

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And we wonder why education in the USA suffers. You just answered his college algebr take home test question for him.

One of the keys to learning math, is sitting down and doing it yourself.

-Dana

10. ### devildog2067

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No offense, but this is a 6th grade math problem. If you can't do it with a piece of paper and a pencil, you need to learn how.

Calculators are for AFTER you learn how to do it, not to do it for you.

11. ### devildog2067

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Bah. Now I feel like a jerk for saying that. My wife always tells me I'm a big softie when it comes to teaching, I guess she's right.

Here's the problem you posted:

$image=http://latex.codecogs.com/gif.latex?%5Cleft%28%5Cleft%28%5Cfrac%7B7%7D%7B10%7D%20%5Cright%20%29%5E3%20-%20%5Cleft%28%5Cfrac%7B3%7D%7B8%7D%20%5Cright%20%29%5E2%20-%20%5Cfrac%7B1%7D%7B5%7D%5Cright%29-%5Cleft%28%5Cleft%28%5Cfrac%7B-1%7D%7B10%7D%20%5Cright%20%29%5E3%20-%20%5Cleft%28%5Cfrac%7B3%7D%7B8%7D%20%5Cright%20%29%5E2%20-%20%5Cfrac%7B1%7D%7B5%7D%5Cright%29%20%5C%5C&hash=5a0d35cdd44a74639a63bd6442365a14$

First thing you need to do is distribute the negative sign in between the two parenthesis:

$image=http://latex.codecogs.com/gif.latex?%5Cleft%28%5Cleft%28%5Cfrac%7B7%7D%7B10%7D%20%5Cright%20%29%5E3%20-%20%5Cleft%28%5Cfrac%7B3%7D%7B8%7D%20%5Cright%20%29%5E2%20-%20%5Cfrac%7B1%7D%7B5%7D%5Cright%29+%5Cleft%28-%5Cleft%28%5Cfrac%7B-1%7D%7B10%7D%20%5Cright%20%29%5E3%20+%20%5Cleft%28%5Cfrac%7B3%7D%7B8%7D%20%5Cright%20%29%5E2%20+%20%5Cfrac%7B1%7D%7B5%7D%5Cright%29%20%5C%5C&hash=d304edc94f9850cef77a625f9a8d9ca7$

Now that you've done this, you can get rid of the big outside parenthesis:

$image=http://latex.codecogs.com/gif.latex?%5Cleft%28%5Cfrac%7B7%7D%7B10%7D%20%5Cright%20%29%5E3%20-%20%5Cleft%28%5Cfrac%7B3%7D%7B8%7D%20%5Cright%20%29%5E2%20-%20%5Cfrac%7B1%7D%7B5%7D-%5Cleft%28%5Cfrac%7B-1%7D%7B10%7D%20%5Cright%20%29%5E3%20+%20%5Cleft%28%5Cfrac%7B3%7D%7B8%7D%20%5Cright%20%29%5E2%20+%20%5Cfrac%7B1%7D%7B5%7D%20%5C%5C&hash=abfb826b02e4c09d4be427dc9a1a3a8c$

Since addition is commutative, you can rearrange the terms:

$image=http://latex.codecogs.com/gif.latex?%5Cleft%28%5Cfrac%7B7%7D%7B10%7D%20%5Cright%20%29%5E3%20-%5Cleft%28%5Cfrac%7B-1%7D%7B10%7D%20%5Cright%20%29%5E3%20+%20%5Cleft%28%5Cfrac%7B3%7D%7B8%7D%20%5Cright%20%29%5E2%20-%20%5Cleft%28%5Cfrac%7B3%7D%7B8%7D%20%5Cright%20%29%5E2+%20%5Cfrac%7B1%7D%7B5%7D-%20%5Cfrac%7B1%7D%7B5%7D%20%5C%5C&hash=b5b3228bf07753d39a56f2b12c79736d$

Now it should be obvious that the pairs of terms with 3/8 and 1/5 cancel each other. That leaves the two terms that are fractions with 10 on the bottom that you have to expand:

$image=http://latex.codecogs.com/gif.latex?%5Cleft%28%5Cfrac%7B7%7D%7B10%7D%20%5Cright%20%29%5E3%20-%20%5Cleft%28%5Cfrac%7B-1%7D%7B10%7D%20%5Cright%20%29%5E3&hash=b16cacd0c3b5d4d636beb06a06e1eb8e$

12. ### devildog2067

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Negative 1 to the third power is still negative one: (-1)(-1)(-1) = -1. Also, you have a common denominator, so you can write:

$image=http://latex.codecogs.com/gif.latex?%5Cfrac%7B7%5E3+1%7D%7B10%5E3%7D%20%3D%20%5Cfrac%7B344%7D%7B1000%7D&hash=6cdc3169be94ed99e03ecba526aa28e2$

Again--no offense, but if you're taking a class on this stuff you should be able to do this in under 30 seconds with just paper and a pencil. Practice, practice, practice.

EDITED TO ADD: I notice that this answer doesn't seem to be the same as what you said Google said... if you typed it into Google the way you posted it, you might have gotten the order of operations wrong. You MUST understand what you're doing before you allow tools to do it for you, or you will not understand what the possible failure modes of the tool are.

Last edited: Apr 6, 2012
13. ### cowboywannabeyou savvy?

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no, if you read my earlier post i had the answer in my post before he did. the first problem was one i just made up. the second one i answered showing the franctional answer which is what google math doesnt show. but thanks for you help just the same.

Last edited: Apr 6, 2012
14. ### douggmc

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Last edited: Apr 6, 2012
15. ### devildog2067

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I think his point was, you shouldn't need google to show you how to do something you should be able to, quite literally, do in your head.

Last edited: Apr 6, 2012

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After all these years, I still tremble when I see these kinds of problems. My palms sweat - I get tunnel vision. Everyone is turning their pages and I'm still on problem one.

17. ### KhufuPharaoh

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Yes. All the modern tools tend to help industry and harm students.

For example, if I am paying an engineer, I hope he isn't spending hours solving equations when MathCAD is readily available. I hope I am not paying an accountant to do the same ledger over and over when excel works well.

But, I also expect that the engineer KNOWS how to solve the equation without MathCAD because that is where the understanding comes from.

As another example, Finite Element Analysis can be used to fine tune designs, but I sure hope an engineer follows basic engineering principles BEfORE he plugs something into FEA. They should have a pretty good idea about beam loading without FEA.

It is important to be able to do the math without a calculator so one understands HOW it is done and not just an answer.

-Dana