Question

what steps someone would take to use your method (substitution)

and a clear argument stating the reason why your method is better than the other ones. (in other words, come up with a few good sentences that explain why you choose your method and why others should too!)

Answer 1

I have no idea why YOU chose substitution. However, here are ideas from a lot of other people.

http://www.google.com/webhp?source=search_app#hl=en&sugexp=les%3B&gs_rn=1&gs_ri=serp&pq=volume%20of%20a%20cylinder&cp=10&gs_id=16&xhr=t&q=method+substitution&es_nrs=true&pf=p&tbo=d&sclient=psy-ab&oq=method+sub&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=c4a6a840dc754efa&biw=711&bih=453

Answer 2

the teacher said i had to do substitution she said it was easier

Answer 3

Whether to use substitution or elimination becomes a judgement call. Sometimes one is easier, at other times not.

e.g.
2x + y = 15
3x +7y = 12

In this case , change the first to y = 15-2x and use substution, clearly easier

e.g

3x + 5y = 9
4x - 3y = 20

Here I would NOT use substitution
multiply 1st by 3 and the 2nd by 5 , then add

etc.

If one of variables has a coefficient of 1 or -1, then substitution is a good and quick method, otherwise it is not easier.