- #1
Jamin2112
- 986
- 12
Homework Statement
Or so it seems. Here are 2 that I'm stuck on:
3.11. Use induction on n to prove that a set of n elements has 2n subsets.
3.35. Let q be a real number other than 1. Use induction on n to prove that ∑qi = (qn-1)/(q-1).
[the summation goes from i=0 to n-1]
Homework Equations
Proof by induction means proving P(1) is true, and then proving P(n) true ---> P(n+1) true.
(Which I still don't understand completely. It seems like you could just choose a statement P(n) which is true when n=1, and then you're just proving that P(n+1) is true, under the assumption that P(n) is true for all n)
The Attempt at a Solution
A={}
The possible subsets are: {}
So the number of possible subsets are: 1=20
A={a1}
The possible subsets are: {a1} , {}
So the number of possible subsets are: 2=21
A={a1, a2}
The possible subsets are: {a1, a2} , {a1}, {a2}, {}
So the number of possible subsets are: 4=22
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Okay, so I believe that formula. I know that {} and A are subsets of A, plus the other n-2 possibilities. But I need some sort of formula for P(n), some inequality or summation or something. How do I do this?
The other problem is just hard. ¡Ayudáme, amigos!