Consider polynomials of degree at most , each of whose coefficients is an element of . How many such polynomials satisfy ?
Pick one
Solutions — 2
Solution 1
Suppose that This problem is equivalent to counting the ordered quadruples where all of and are integers from through such that Let and Note that both of and are integers from through Moreover, the ordered quadruples and the ordered quadruples have one-to-one correspondence.
We rewrite the given equation as or By the stars and bars argument, there are ordered quadruples
~pieater314159 ~MRENTHUSIASM
Solution 2
1. Let . We are given that .
2. Substituting into , we get:
3. We need . Rearranging, we get:
4. Let . Then . The possible values of range from 9 to 18 (since are digits from 0 to 9).
5. For each fixed , we need to count the number of valid pairs and such that:
6. The number of pairs such that is (since and are digits from 0 to 9).
7. The number of pairs such that is (since and are digits from 0 to 9).
8. Therefore, for each , the number of valid polynomials is:
9. We need to sum this product over all possible values of from 9 to 18:
10. Simplifying the sum:
11. Calculating each term:
12. Summing these values:
The final answer is