1984 AIME Problems/Problem 12
A function is defined for all real numbers and satisfies and for all . If is a root for , what is the least number of roots must have in the interval ?
If , then substituting gives . Similarly, . In particular,
Since is a root, all multiples of are roots, and anything congruent to are also roots. To see that these may be the only integer roots, observe that the function satisfies the conditions and has no other roots.
In the interval , there are multiples of and numbers that are congruent to , therefore the minimum number of roots is .
Solution 2 (non-rigorous)
We notice that the function has reflectional symmetry across both and . We also use the fact that is a root. This shows that and are also roots. We then apply the reflection across the other axis to form as roots. Continuing this shows that the roots are or . There are 200 positive roots and 200 negative roots. 0 is also a root, and adding these gives a result of .
Solution by a1b2
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