When equal and equi-spaced forces are summed on y-axis what is vector sum? How do we derive the formula
n−1∑k=1sinπkn=cotπ2n
( Formula given by Marco Cantarini in comments below. )
By a similar token, can
n−1∏k=1sinπkn=2n2n
represent some physics force multiplication situation or any generalized law in which
this analogue is valid? (Formula mentioned by Jack D'Aurizio in a recent thread
Geometric proof of sin60∘sin40∘...).
Answer
With some preliminary manipulations, both the identities can be derived by regarding
ζk=sinπkn
as roots of a suitable Chebyshev polynomial, then applying Vieta's formulas - relations between the roots and the coefficients of a monic polynomial.
No comments:
Post a Comment