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seen Mar 1 at 7:24

Apr
11
awarded  Popular Question
Jun
22
awarded  Popular Question
Feb
27
comment Wolfram Alpha's Mysterious Trig Abilities…
I like this because it's so visual. Accepted!
Feb
27
accepted Wolfram Alpha's Mysterious Trig Abilities…
Feb
27
suggested suggested edit on How would I apply the limit laws to $\lim_{x\to 2}\frac{(3x-6)\sqrt{x^2+1}}{5x-10}$?
Feb
27
comment Wolfram Alpha's Mysterious Trig Abilities…
why do this instead of using the sum->product formula?
Feb
27
comment Wolfram Alpha's Mysterious Trig Abilities…
I don't know why this got so many votes... It was just a small error in arithmetic.
Feb
27
revised Wolfram Alpha's Mysterious Trig Abilities…
deleted 250 characters in body
Feb
27
comment Wolfram Alpha's Mysterious Trig Abilities…
@Ted forgot to omit that irrelevant part of the question. Fixed
Feb
27
revised Wolfram Alpha's Mysterious Trig Abilities…
added 2 characters in body
Feb
27
asked Wolfram Alpha's Mysterious Trig Abilities…
Jan
9
awarded  Popular Question
Aug
17
comment Ways to define a curve
@JayeshBadwaik Yes, they are
Aug
17
awarded  Promoter
Aug
17
accepted Calculating Distance of a Point from an Ellipse Border
Aug
17
revised Ways to define a curve
added 160 characters in body; edited tags
Aug
17
accepted Summation of an Arithmetic, Parametric Sequence
Aug
17
comment Summation of an Arithmetic, Parametric Sequence
Ok, but that still doesn't answer my first question. How EXACTLY did you get from D(n,r) = D(n−1,r) +(n−r) to the addition of those two summations (i and j)?
Aug
16
comment Summation of an Arithmetic, Parametric Sequence
Also, if I may prick your brain =), how did you so quickly realize that D(n,r) equaled D(n-r,0) + D(r,r) or that D(n,n) equaled n(n+1)/2 or that D(n-1, r) + (n-r) equaled D(n-1,r-1) + r? Are there some generic rules I'm not aware of?
Aug
16
comment Summation of an Arithmetic, Parametric Sequence
Thanks for sharing your insight, but I'm still a bit confused. I thought you'd have to take D(n-1,r) out of the equation in order to perform summation since it merely acts as a symbol for recursive addition of all preceding terms (which is taken care of by the summation). According to your answer, SUM(n-r) is equal to SUM(D(n-1,r-1)) while SUM(r) is equal to SUM(D(n-1,r)). I don't see how D(n-1,r) and D(n-1,r-1) could have any direct value considering they are just indicators that the sequence needs to be summed.