SOLUTION: prove by mathematical induction: 1^5 + 2^5 + 3^5 + ... + n^5 = (1/12)n^2(n+1)^2(2n^2 + 2n -1)

Algebra ->  Complex Numbers Imaginary Numbers Solvers and Lesson -> SOLUTION: prove by mathematical induction: 1^5 + 2^5 + 3^5 + ... + n^5 = (1/12)n^2(n+1)^2(2n^2 + 2n -1)      Log On


   



Question 1184007: prove by mathematical induction:
1^5 + 2^5 + 3^5 + ... + n^5 = (1/12)n^2(n+1)^2(2n^2 + 2n -1)

Answer by math_helper(2461) About Me  (Show Source):
You can put this solution on YOUR website!
prove by mathematical induction:
1^5 + 2^5 + 3^5 + ... + n^5 = (1/12)n^2(n+1)^2(2n^2 + 2n -1)
--------

Base case: 1%5E5 = 1
%281%2F12%29%281%29%5E2%281%2B1%29%5E2%282%281%29%5E2%2B2%281%29-1%29+ = %281%2F12%29%284%29%283%29 = 1
Base case holds.

Hypothesis:
Assume 1%5E5+%2B+2%5E5+%2B+3%5E5 + ... + n%5E5 = +%281%2F12%29n%5E2%28n%2B1%29%5E2%282n%5E2+%2B+2n+-1%29+ for n=k. (*)

Step case: Let n=k+1
[ +1%5E5+%2B+2%5E5+%2B+3%5E5 + ... + k%5E5 ] + %28k%2B1%29%5E5
... use hypothesis on terms within [ ] ...
= +%281%2F12%29k%5E2%28k%2B1%29%5E2%282k%5E2+%2B+2k+-1%29+ + +%28k%2B1%29%5E5
... this reduces to (you can factor %28k%2B1%29%5E2 then use a factoring website for the rest) ... (see NOTE)
= +%281%2F12%29%28k%2B1%29%5E2%28%28k%2B2%29%5E2%282k%5E2%2B6k%2B3%29%29+
The proof is complete here, but it is not obvious, so
let u=k+1 --> k=u-1
= +%281%2F12%29%28u%29%5E2%28u%2B1%29%5E2%282%28u-1%29%5E2%2B6%28u-1%29%2B3%29+
= +%281%2F12%29%28u%29%5E2%28u%2B1%29%5E2%282u%5E2%2B2u-1%29+
Proof complete
NOTE: I admit, there may be an easier path here. If other tutors (or the student) wish to find it, more power to them. I gave the general idea...
If this helps the student, thanks are appreciated.