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A (k) =the closed interval [-10+Sin [k], 10+Sin [k]] How do I can create a list of the first 20 of such interval The find the intersection of the first 14 of them

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  • $\begingroup$ Is k integer? Use Range and IntervalIntersetcion[] $\endgroup$ – Dr. belisarius Dec 1 '13 at 17:01
  • $\begingroup$ Yes k is an integer number $\endgroup$ – mais Dec 1 '13 at 17:07
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c = IntervalIntersection @@ (Array[ Interval[{-10 + Sin[#], 10 + Sin[#]}] &, {20}][[;; 14]])

Graphics[{Array[Line[{{-10 + Sin[#], #}, {10 + Sin[#], #}}] &, {14}], 
         Red, c /. Interval[{x_, y_}] -> Line@{{x, 0}, {y, 0}}}]

Mathematica graphics

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The code

ak = N[Table[Interval[{-10 + Sin[k], 10 + Sin[k]}], {k, 1, 20}]];

computes the first 20 as intervals. Remove the N[ ] wrapper for the exact values. You can then compute the intersection of the first 14 as closed intervals with

IntervalIntersection @@ ak[[1;;14]]

Finally this is the correct intersection: Interval[{-9.00939, 9.00001}]

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  • $\begingroup$ What's @ means? ? $\endgroup$ – mais Dec 1 '13 at 17:14
  • $\begingroup$ @Nana @@ -Apply. Difference between @ and @@. $\endgroup$ – Kuba Dec 1 '13 at 17:14
  • $\begingroup$ .. thank you :-) $\endgroup$ – mais Dec 1 '13 at 17:18
  • $\begingroup$ I see the problem 1 sec $\endgroup$ – J. W. Perry Dec 1 '13 at 17:20
  • $\begingroup$ I'm really confuse now... what is the corect code in this case? $\endgroup$ – mais Dec 1 '13 at 17:21
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We can use properties of Interval earlier:

f = Sin[#] + Interval[{-10, 10}]&;
IntervalIntersection @@ Array[f, 14] // N
Interval[{-9.00939, 9.00001}]
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You can answer this question without knowing anything about interval functions: the intersection of all the intervals is the interval between (10-largest value of Sin) and (10+smallest value of Sin). With Sin assuming integer values between 1 and 14, this is:

{10 - Max[Sin[Range[14]]], 10 + Min[Sin[Range[14]]]}
{10 - Sin[14], 10 + Sin[11]}//N
{9.00939, 9.00001}
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