Difference between revisions of "2006 SMT/General Problems/Problem 16"
(Created page with "==Solution== The condition we are looking for is <math>35(n-1)\equiv 0 \mod 360</math>, because if any other <math>A_n = A_1</math> than <math>35(n-1)</math> must be a multip...") |
(→Solution) |
||
(2 intermediate revisions by the same user not shown) | |||
Line 1: | Line 1: | ||
+ | ==Problem== | ||
+ | Points <math> A_1, A_2, \cdots </math> are placed on a circle with center <math> O </math> such that <math> \angle OA_nA_{n+1}=35^\circ </math> and <math> A_n\not=A_{n+2} </math> for all positive integers <math> n </math>. What is the smallest <math> n>1 </math> for which <math> A_n=A_1 </math>? | ||
+ | |||
+ | |||
==Solution== | ==Solution== | ||
− | The condition we are looking for is <math> | + | The condition we are looking for is <math>110(n-1)\equiv 0 \mod 360</math>, because if any other <math>A_n = A_1</math>, than <math>110(n-1)</math> must be a multiple of 360. This is because the central angle formed between two consecutive points is 110 degrees, and because we have rotated <math>(n-1)</math> times by the time we place <math>A_n</math>. |
− | |||
− | |||
− | + | <cmath>110(n-1)\equiv 0\mod 360 \Rightarrow 10(n-1)\equiv 0\mod 360 \Rightarrow x\equiv 37\mod 360</cmath> | |
+ | We want the first <math>A_n</math> that satisfies the conditions from the problem, therefore, our answer is <math>n=37</math> or <math>\boxed{A_{37}}</math> |
Latest revision as of 11:43, 15 January 2020
Problem
Points are placed on a circle with center such that and for all positive integers . What is the smallest for which ?
Solution
The condition we are looking for is , because if any other , than must be a multiple of 360. This is because the central angle formed between two consecutive points is 110 degrees, and because we have rotated times by the time we place .
We want the first that satisfies the conditions from the problem, therefore, our answer is or