Math Is Fun Forum

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

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)

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

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 (2013-03-06 09:44:54)

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

muxdemux

Member

Registered: 2012-12-23

Posts: 80

Re: Evaluate algebraic expression

Disagree

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

Re: Evaluate algebraic expression

Mux, the supposed answer is -54...

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Evaluate algebraic expression

hi muxdemux

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

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

Re: Evaluate algebraic expression

What is your answer ?

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

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 ?

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?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Evaluate algebraic expression

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

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

Bob

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

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

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 ?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

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

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

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 ^^

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

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

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

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

Yes, It's ok.

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 )

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Evaluate algebraic expression

We all need our foundations to be destabilized sometimes. 

bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

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 ...

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.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Evaluate algebraic expression

Hi Al-Allo

are you people mathematicians or proffesors ?

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

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

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

Re: Evaluate algebraic expression

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