# Homework Help: How to factor when no common factors?

1. Apr 22, 2010

### Gringo123

How can I foctorise / factor this given that 25 and 49 share no common factors?

25x2 - 49y2

2. Apr 22, 2010

### Mentallic

Re: Factorising

Note that 25=52 and $$a^nb^n=(ab)^n$$

3. Apr 22, 2010

### Staff: Mentor

Re: Factorising

This is a difference of squares.

4. Apr 22, 2010

### iRaid

Re: Factorising

(a+b)(a-b) = a2-b2

Make sure to make a and b not squared..So instead of 25, 5.

5. Apr 23, 2010

### Mentallic

Re: Factorising

Neither do x2 and y2 share any common factors, so this should imply you're looking for another factoring method other than finding a common factor. In this case, difference of two squares.

6. Apr 23, 2010

### Gringo123

Re: Factorising

Thanks everyone. So am I right in saying that the answer would be:
(5x - 7y) (5x + 7y)
?

7. Apr 23, 2010

### Mentallic

Re: Factorising

8. Apr 23, 2010

### iRaid

Re: Factorising

That would be correct.

9. Apr 24, 2010

### Gringo123

Re: Factorising

Thanks Raid!

10. Apr 25, 2010

### Mentallic

Re: Factorising

If you prefer the easier way out (and the lazy approach at that), that's up to you, but you should reconsider becoming more trusting in yourself and not always of those around you.

In this problem, if you expanded your answer it will confirm whether you factorized correctly or not. In other topics you have been studying, for example the quadratic factoring, if asked to solve

$$x^2-x-6=0$$ and you factorize it as so $$(x-3)(x+2)$$ you can check by expanding, or even plug your values x=3 and x=-2 into the quadratic to see if it's correct.

I'm just saying that there are ways to check your work so you become more independent with your mathematics. Having low confidence in your answers would be bad in tests, considering you're all alone in those situations.