Difference between revisions of "2008 AIME I Problems/Problem 7"
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The difference between consecutive squares is <math>(x + 1)^2 - x^2 = 2x + 1</math>, which means that all squares above <math>50^2 = 2500</math> are more than <math>100</math> apart. | The difference between consecutive squares is <math>(x + 1)^2 - x^2 = 2x + 1</math>, which means that all squares above <math>50^2 = 2500</math> are more than <math>100</math> apart. | ||
− | Then the first <math>26</math> sets (<math>S_0,\cdots S_{25}</math>) each have at least one perfect square. Also, since <math>316^2 < 100000</math> (which | + | Then the first <math>26</math> sets (<math>S_0,\cdots S_{25}</math>) each have at least one perfect square because the differences between consecutive squares in them are all less than <math>100</math>. Also, since <math>316</math> is the largest <math>x</math> such that <math>x^2 < 100000</math> (<math>100000</math> is the upper bound which all numbers in <math>S_{999}</math> must be less than), there are <math>316 - 50 = 266</math> other sets after <math>S_{25}</math> that have a perfect square. |
There are <math>1000 - 266 - 26 = \boxed{708}</math> sets without a perfect square. | There are <math>1000 - 266 - 26 = \boxed{708}</math> sets without a perfect square. |
Latest revision as of 21:59, 2 January 2021
Contents
[hide]Problem
Let be the set of all integers such that . For example, is the set . How many of the sets do not contain a perfect square?
Solution
The difference between consecutive squares is , which means that all squares above are more than apart.
Then the first sets () each have at least one perfect square because the differences between consecutive squares in them are all less than . Also, since is the largest such that ( is the upper bound which all numbers in must be less than), there are other sets after that have a perfect square.
There are sets without a perfect square.
Video Solution
~IceMatrix
See also
2008 AIME I (Problems • Answer Key • Resources) | ||
Preceded by Problem 6 |
Followed by Problem 8 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
All AIME Problems and Solutions |
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