WHich of these steps is wrong?

[AgaBoogaBoo]

(1) x = 2
(2) 3x - 2x = 2
(3) 3x = 2x + 2
(4) x^2 + 3x = x^2 + 2x + 2
(5) x^2 + 3x - 10 = x^2 + 2x - 8
(6) (x - 2)(x + 5) = (x - 2)(x + 4)
(7) x + 5 = x + 4
(8) 1 = 0

I noticed that if you substitute x with 2 in steps 5 and 6 that you get different answers, I'm guessing that is where the error is, but I just don't see it

 

[dighn]

6->7 is wrong

division by 0

 

[Chu]

in line (6), you divided by zero. Since x = 2, (x-2)(x+5)/(x-2) = 0/0 = under

 

[AgaBoogaBoo]

I'm confused, division by zero? How so?

I haven't ever heard division by zero used that way

 

[AgaBoogaBoo]

Originally posted by: Chu
in line (6), you divided by zero. Since x = 2, (x-2)(x+5)/(x-2) = 0/0 = under

ah, k, that makes sense, thanks!

 

[AgaBoogaBoo]

Thanks Dighn and Chu!

:beer: :cockie;

 

[rgwalt]

Since x = 2 you cannot cancel (x-2) from both sides in step 6 since it results in a division by 0. Step 6 shows that 0 = 0.

R

 

[dighn]

Originally posted by: AgaBooga
:beer: :cockie;

:Q

 

[Ketteringo]

In line 6 you MULTIPLY by 0

 

[AgaBoogaBoo]

Originally posted by: dighn

Originally posted by: AgaBooga
:beer: :cockie;

:Q

musta been a typo, woops

 

[jagec]

Originally posted by: Ketteringo
In line 6 you MULTIPLY by 0

yes, but to get to line 7 from line 6, you have to divide by zero, which is bad.