We , means Human and Computer both can Solve only finite problems [ Problems which can be solved by finite number of Computation(s) ] .
There are some problems which can't be solved by Any Human / Computer in Countable time [ They are called Undecidable Problem ] .
So we will solve problems Using following Steps : ->
1. Determine whether Problem is Decidable .
2. If Decidable then see whether it is finite or not.
3. If finite then solve it in finite steps else follow :-
a) Induction or
b) Contradiction which one is Useful to reduce problem in finite Domain
Induction:-
Chose a property say P s.t. if it is valid for the whole set of problem then we can obviously say that the
problem is solved .
Find a Bijection f from problem set to set of Natural Number N s.t Problem Set = f(n)
where n ∈ N
Basis: Prove it for a Small Cluster Of Problem Set .
Induction Step : Prove that if for Problem set f(1),f(2)...f(n) P holds then for f(n+1) also it holds.
Now we can say that P holds for the Whole Problem Set .
That means Problem Solved.
Example :- Prove that f(n)=1+2+...n =n(n+1)/2
Basis: n=1 it is true
Induction Step : f(n)=n(n+1)/2
f(n+1)=f(n)+n+1= (n+1)(n+2)/2 i.e true
Proved.
Contradiction: Let the opposite is true . Then do the calculation with other Properties and eventually you will
find that a contradiction will arrive .
Example:- x=2 y=3 z=x+y then show z=5
let z!=5
x+y=2+3=5
z=x+y
5!=5 contradiction .
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