Question

which of the following statements is (are) true for all the positive integers?
1) 1+2+3+4+...+ n= n(n+1)/2
2) 1+3+5+...+(2n-1)=n^2

Answer 1

Try a few cases, if you find a single case that is not true, the statement is false.
If all cases you tried give correct answers, then it is a little more difficult.

Do you know mathematical induction?

If you do, you can check that which one(s) is/are true and use mathematical induction to prove that it is true for ALL positive integers.

If not, you can only try a few verifications and "conclude" that they are true.

Answer 2

there both true never miiind

Answer 3

Correct.