Related to Q16675:
Find the number of intersection points
of graph sin x=(x/(10)).
Let′s see sin x = (x/n) with n>1.
For n≤1 there is one intersection point.
Let x=2kπ+t with k∈N ∧ t∈[0,2π]
sin x=sin t
cos x=cos t
we find the point on f(x)=sin x where its
tangent is g(x)=(x/n).
f′(x)=cos x=cos t
g′(x)=(1/n)
cos t=(1/n)
t=cos^(−1) (1/n)
sin t=(n/(√(n^2 +1)))
so that f(x) intersects with g(x),
((sin x)/x)≥(1/n)
⇒n sin x≥x
⇒n sin t≥2kπ+t
⇒k≤((n sin t −t)/(2π))=(((n^2 /(√(n^2 +1)))−cos^(−1) (1/n))/(2π))
k_(max) =⌊(((n^2 /(√(n^2 +1)))−cos^(−1) (1/n))/(2π))⌋
number of intersecting points is
m=2×2(k_(max) +1)−1=4k_(max) +3
for n=10
k_(max) =⌊(((n^2 /(√(n^2 +1)))−cos^(−1) (1/n))/(2π))⌋
=⌊((((10^2 )/(√(10^2 +1)))−cos^(−1) (1/(10)))/(2π))⌋=⌊1.35⌋=1
⇒m=4×1+3=7
for n=20
k_(max) =⌊((((20^2 )/(√(20^2 +1)))−cos^(−1) (1/(20)))/(2π))⌋=⌊2.94⌋=2
⇒m=4×2+3=11
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