+0  
 
+1
64
10
avatar+30 

Hi, I need help with this problem, I tried every possible way and got 17/5 every time, I even checked Wolfram Alpha and it also says the answer is 17/5, Aops says this answer is wrong, plz show me what I did wrong with my calculations!

 Jan 29, 2021
 #1
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0

x^2 -11x+28      + 6 +3x-2x-x^2   = 0 (?)

      -10x +34   

       10x = 34

           x = 34/10 = 17/5

 Jan 29, 2021
 #2
avatar+30 
0

It says that's wrong.

 Jan 29, 2021
 #8
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That's why I added the  =0 (?)     But you didn't respond !

Guest Jan 29, 2021
 #3
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+1

Without doing any algebra, I can already tell that your answer of 17/5 cannot possibly be correct. This expression requires multiplication and addition of integers and variables, so it is impossible that the answer would yield a rational number.

 

Anyway, let's see what the real answer is, shall we?
 

\((x-4)(x-7) + (3-x)(2+x)\\ x^2-7x-4x+28+6+3x-2x-x^2\\ -10x+34\)

 

This is as far as we can simplify this expression. Remember that this expression is not an equation. I believe your mistake was that you set this expression equal to 0 and solved. 

 Jan 29, 2021
 #4
avatar+30 
0

Oh, ok, thanks for the help.

 Jan 29, 2021
 #5
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Yes, you are welcome. Just remember not to convert an expression into an equation. This is a fairly common mistake. Good luck on your future algebraic adventures!

Guest Jan 29, 2021
 #6
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0

 

(x – 4)(x – 7) + (3 – x)(2 + x)  

 

(x2 – 11x + 28) + (–x2 + x +6)  

 

x2 – x2 – 11x + x + 28 + 6  

 

–10x + 34  

 

simplified this is  2(17 – 5x)  

 

Nothing in the problem you provided said to set the expression equal to zero and solve for x.  

.

 Jan 29, 2021
 #7
avatar+267 
+2

note for the future: on aops, "simplify" on equations with variables means "combine like terms then write out the equation in terms of the variable". 

 

I use aops so trust me. I've done like 100 questions on simplifying expressions. 

 Jan 29, 2021
edited by KitSoundwave  Jan 29, 2021
edited by KitSoundwave  Jan 29, 2021
 #9
avatar+30 
0

I use Aops too.

 Feb 4, 2021
 #10
avatar+30 
0

btw, I figured out the answer.

 Feb 4, 2021

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