0 like 0 dislike
0 like 0 dislike
Where am I going wrong

7 Answers

0 like 0 dislike
0 like 0 dislike
Hi u/scillywoba,

**You are required to explain your post and show your efforts. _(Rule 1)_**

Please add a comment below explaining your attempt(s) to solve this and what you need help with **specifically**. If some of your work is included in the image or gallery, you may make reference to it as needed. See the sidebar for advice on 'how to ask a good question'. Don't just say you need help with it.

**Failure to follow the rules and explain your post will result in the post being removed**


*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/askmath) if you have any questions or concerns.*
0 like 0 dislike
0 like 0 dislike
When you multiply something into a sum, you need to multiply with every term. Like this:   
(a + b)x = ax + bx   
Similarly for when you divide. Thus in the division on the top row can't cross out the x's like that, because then you skip the division of the second term.
0 like 0 dislike
0 like 0 dislike
You can't cancel terms that are inside a sum.

You can only cancel terms that are factors (part of a product).

(x^3 + ux)/x^3 does not have a product in numerator.

But you can factorize/factorise the numerator to make it a product of x and (x^2 + u).

= (x * (x^2 + u)) / (x * x^2 )

= (~~x~~ * (x^2 + u)) / (~~x~~ * x^2 )

= (x^2 + u) / x^2

The common factor x in each of the terms in the numerator can be pulled out as a factor using distributive property. Then you do see factor x in top and bottom that cancels, because x/x = 1.


A simpler example:

(5x + 3)/x is equal to 5x/x + 3/x = 5/1 + 3/x = 5 + 3/x.

You can't say (5x + 3)/x = (5~~x~~ + 3)/~~x~~ = (5(1) + 3)/1 = 8
0 like 0 dislike
0 like 0 dislike
As someone else has said, you can’t cancel part of addition or subtraction. If you have (2+7)/2 can you cancel the 2’s leaving the answer being 7? No.

So on your first line you can’t cancel the x^3 .

Not sure why you are multiplying the top and bottom by x^3 on the second line? Where does the x^3 on the bottom go?
0 like 0 dislike
0 like 0 dislike
Top equation should be:

(x^3 + ax)/x^3 = 1 + (a/x^2 )

Basically, as others said, you can only cancel factors, not addition.
0 like 0 dislike
0 like 0 dislike
This is hideous to look at
0 like 0 dislike
0 like 0 dislike
(x^3 + ux)/x^3 =/= ux

Because if you factor the numerator, you get:

x(x^2 + u)

As there is only one x in both terms in the numerator.

So you’d really get (x^2 + u)/x^2, which can be rewritten as 1 + u / x^2

Realistically this is about as simplified as you can get without any other information

No related questions found

29.6k questions

121k answers


33.7k users

OhhAskMe is a math solving hub where high school and university students ask and answer loads of math questions, discuss the latest in math, and share their knowledge. It’s 100% free!