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#1 2013-03-06 09:20:55

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Evaluate algebraic expression

Hi

-a+3*(a-c)+c^2-a*c^2

a=-2

b=4
c=-5

i keep getting -64, would you agree with me or disagree ?

thanks

Last edited by Al-Allo (2013-03-06 09:25:35)

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#2 2013-03-06 09:41:19

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,121

Re: Evaluate algebraic expression

hi Al-Allo

No I don't agree.

It looks like you are doing -(a*c)^2 rather than -a times (csquared)

I suggest you do these steps separately and then add them:

-a

3*(a-c)

c^2

(-a)*c^2

Bob

Last edited by bob bundy (2013-03-06 09:44:54)


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#3 2013-03-06 09:43:23

muxdemux
Member
Registered: 2012-12-23
Posts: 80

Re: Evaluate algebraic expression

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#4 2013-03-06 09:48:14

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Re: Evaluate algebraic expression

Mux, the supposed answer is -54...

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#5 2013-03-06 09:49:22

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,121

Re: Evaluate algebraic expression

hi muxdemux

That's not what I'm getting???

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#6 2013-03-06 09:53:35

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Re: Evaluate algebraic expression

What is your answer ?

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#7 2013-03-06 09:55:09

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Re: Evaluate algebraic expression

I found this website http://www.myalgebra.com/algebra_solver.aspx

And It gets also -64 And not -54 ....Any suggestions ?

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#8 2013-03-06 10:14:55

muxdemux
Member
Registered: 2012-12-23
Posts: 80

Re: Evaluate algebraic expression

I'm getting 86 with the algebra solver you linked.

Sorry about my previous post. I subbed into the equivalent expression Wolfram Alpha came up with instead of the original. I don't see any reason the answer should be different though.

Why don't you show your working, Allo?

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#9 2013-03-06 10:15:23

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,121

Re: Evaluate algebraic expression

Sorry muxdemux, I was wrong before.  I do get the same as you.  shame

I didn't follow your working though.  I'm glad you explained where it came from.  smile

Bob

Last edited by bob bundy (2013-03-06 10:27:13)


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#10 2013-03-06 10:26:41

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Re: Evaluate algebraic expression

Ok, I got the same answer as you but may you explain me something ?

Why do you put-5 in to parantheses ?

it doesn't have any, -5^2 = -(5X5)=-25

How is this wrong ?

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#11 2013-03-06 10:29:12

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,121

Re: Evaluate algebraic expression

Because minus 5 squared means multiply minus 5 by itself.  ie. -5 x -5 = +25

are not the same thing.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#12 2013-03-06 10:36:18

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Re: Evaluate algebraic expression

Ok...That's weird, I thought that it needed to be specified by parentheses so we could include the minus signs. Oh well, thanks for your help. Neither the exercise or me got it ^^

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#13 2013-03-06 10:39:46

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,121

Re: Evaluate algebraic expression

You are asked to evaluate c^2 (amongst other things of course ... but let's just concentrate on that bit)

So evaluate -5 squared

I put in the bracket to explain why that becomes +25.

Try this on a calculator.

Enter 5, switch it to negative with the +/- button, and store it.

Then do memory recall and press the square button.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#14 2013-03-06 10:43:34

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Re: Evaluate algebraic expression

bob bundy wrote:

You are asked to evaluate c^2 (amongst other things of course ... but let's just concentrate on that bit)

So evaluate -5 squared

I put in the bracket to explain why that becomes +25.

Try this on a calculator.

Enter 5, switch it to negative with the +/- button, and store it.

Then do memory recall and press the square button.

Bob

Yes, It's ok. smile

I understand that but it's just I had that memory which didn't seem to agree with you (Like you were distabilizing my foundations, but it's for my good tongue)

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#15 2013-03-06 10:45:51

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,121

Re: Evaluate algebraic expression

We all need our foundations to be destabilized sometimes.  smile

bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#16 2013-03-06 10:47:38

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Re: Evaluate algebraic expression

Yes, even when it's hard to admit we were wrong. Curiously, are you people mathematicians or proffesors ? If If it's okay with you to answer ...

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#17 2013-03-06 18:21:57

muxdemux
Member
Registered: 2012-12-23
Posts: 80

Re: Evaluate algebraic expression

Neither the exercise or me got it

Maybe... You might want to double check that you typed the equation properly in your original post. (Does your textbook really say

?)

are you people mathematicians or proffesors

I'm just some guy from Australia lol. I'm studying at university right now, but I'm definitely not a professor! I'm not even studying to become a mathematician. Though math is needed in a lot of different subjects.

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#18 2013-03-06 20:11:42

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,121

Re: Evaluate algebraic expression

Hi Al-Allo

Al-Allo wrote:

are you people mathematicians or proffesors ?

I am a retired teacher (of maths).  In French the word  'professeur' means teacher.

muxdemux wrote:

check that you typed the equation properly in your original post

You have a value for 'b' but it isn't used in the question.  Maybe there should be a 'b' in it?

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#19 2013-03-07 03:49:31

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Re: Evaluate algebraic expression

Nah, there isn't any. The b was for other equations.. ^^ Thank you for your help, I love this forum.!

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