## agbyoung Group Title Explain how to find a prime factorization of a number! 2 years ago 2 years ago

1. agbyoung Group Title

I have to write this in an open ended response!

2. JamesJ Group Title

There's how you might write a computer program to do it; and then how a human being does it. Which do you want?

3. agbyoung Group Title

4. JamesJ Group Title

Well, evaluate honestly how you do it. For example, if I asked you for the prime factorization of 720, how would you figure it out?

5. agbyoung Group Title

ugh!

6. JamesJ Group Title

easier one then. What's the prime factorization of 100?

7. jimmyrep Group Title

8. agbyoung Group Title

ok

9. satellite73 Group Title

i do it like steve jobs http://www.wolframalpha.com/input/?i=factor+264575

10. agbyoung Group Title

jimmyrep could you answer this one to?

11. satellite73 Group Title

pick a number. then factor. that is what you have to do, there is no shortcut

12. jimmyrep Group Title

the way i do it is as follows ; if its even divide by 2 if not try 3 if it ends in 5 - try 5 7 etc example: factorise 2360: 2 ) 2360 2 ) 1180 2 ) 590 2 ) 295 5 ) 59 59 is a prime number so 1260 = 2x2x2x2x5x59 or 2^4*5*59

13. satellite73 Group Title

i pick 72 $72=2\times 36=2\times 2\times 18=2\times 2\times 2\times 9=2\times 2\times 2\times 3\times 3=2^3\times 3^2$

14. JamesJ Group Title

$100 = 10^2 = (2 \times 5)^2 = 2^2 \times 5^2$

15. JamesJ Group Title

The way I would actually do 2360 is a little differently; not better or worse, just different. First I'd pull out the 10. Then I see 236 is divisible by 4, so I have $2360 = 10 \times 4 \times 59$ Now 59 is prime so now I have $2360 = (2 \times 5) \times (2 \times 2) \times 59 = 2^3 \times 5 \times 59$ (which IS different from Jimmy's answer, because his is not quite correct.)

16. JamesJ Group Title

If I were writing a computer program, I'd implement an algorithm like jimmy's

17. jimmyrep Group Title

hhmm - oh yes - I put in one 2 too many !!!