I was bored in my Algebra 2 class and wanted to try to illustrate the tan(x) function as an infinite

migongoniwt

migongoniwt

Answered question

2022-06-14

I was bored in my Algebra 2 class and wanted to try to illustrate the tan(x) function as an infinite summation of rational functions.
I recalled that the solution to a rational function's numerator is equivalent to the roots of the function. The denominator's solution is the vertical asymptote(s). Since tan(x) has infinite roots and asymptotes, if I expressed it as a rational function it'd be infinitely long. My teacher suggested just using an infinite summation of rational functions, so I did that instead.
The first thing I did was set up the numerator and denominator so that they could each equal the corresponding roots and asymptotes; since it's (sorta? kinda? maybe) an even function, I just used variations of x ± π for both sides. Given that all roots of tan(x) are whole multiples of pi and all asymptotes are odd multiples of pi/2, I came up with the following equation:
n = x ± n π x ± 2 n 1 ) π 2
Where n is any integer from negative infinity to infinity, my idea is that the end product of this is tan(x). Is this even remotely correct or did I leave something out? Thanks!
(I do recognize that the horizontal asymptote is apparently 1 with this equation, but when I plot a section of this in desmos it seems to pass through y=1 anyway. There might be something going on that I could simplify in terms of rewriting an "x^2" somewhere, or maybe I'm just trippin.)

Answer & Explanation

Sydnee Villegas

Sydnee Villegas

Beginner2022-06-15Added 22 answers

Your idea is good, but the series does not converge.
Actually, from the Mittag-Leffler's theorem (somewhat advanced complex analysis), one has the expansion
tan x = n = 0 8 x ( 2 n + 1 ) 2 π 2 4 x 2 .
Now the quadratic dependence of n in the denominator ensure convergence! Note that the above series correctly diverges at x = ( n + 1 / 2 ) π, and is zero at x = n π

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