# Proof : For every positive integer n, prove that 1+2+...+n=n(n+1)/2.

Problem: For every positive integer n, prove that 1+2+...+n=n(n+1)/2.

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#### Solution Preview

One can use Principle of Mathematical Induction.

for n=1, it is easy to check that both sides of the equation give the same value.

LHS: 1

and RHS: 1(1+1)/2=1

Hence the statement is true for n=1.

Let the statement is true for some ...

#### Solution Summary

A proof is provided. The solution is detailed and well presented.

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