Question

Prove for

Answer 1

Answer:

Step-by-step explanation:

Hello, we want to prove that a proposition depending on n, that we can note P(n), is true for any n positive integer greater than 1. We need to follow several steps.

Step 1 - prove P(1)

For n = 1, n(2n+1)=1*3 =3 so we have

3 = 3, which is obviously true.

First step done!

Step 2 - for $k\geq 1$ we assume P(k) and we need to prove P(k+1)

We assume that 3+7+11+...+(4k-1)=k(2k+1)

so we can write that

3+7+11+...+(4k-1)+(4(k+1)-1)=k(2k+1)+(4k+4-1)=k(2k+1)+4k+3

$=2k^2+k+4k+3\\\\=2k^2+5k+3$

and

(k+1)(2(k+1)+1)=(k+1)(2k+3)

$=k(2k+3)+2k+3\\\\=2k^2+3k+2k+3\\\\=2k^3+5k+3$

These two expressions are the same so it means that P(k+1) is true, meaning that

3+7+11+...+(4k-1)+(4(k+1)-1)=(k+1)(2(k+1)+1)

Step 3 - The conclusion

Finally, we have just proved that

3+7+11+...+(4n-1)=n(2n+1) for any n positive integer > 0

Thank you