Browse · MATH
Printjmc
algebra intermediate
Problem
If is an integer and , find .
Solution
We could subtract to the other side and try to solve the sixth-degree equation, but that would be ugly and we have no guarantee that it would even work. We notice that we can add a to the polynomial without changing its value: We regroup the terms and factor the left side, leaving the alone. To see a different way of obtaining this factorization, we could also group the and terms together and factor, giving: Since is an integer, then and are integers, so they must be factors of . The prime factorization of is . The value must be a square which divides , and we can see that the only squares which divide are and .
If , then , and or . If , it's easy to see from the original equation that it won't work, since the left side of the original equation would be while the right side would be . If , then the left side would equal . So both values of are impossible.
Thus , so and or . If , then we have the left side as . If , then we have as desired. Thus the only possibility for is .
If , then , and or . If , it's easy to see from the original equation that it won't work, since the left side of the original equation would be while the right side would be . If , then the left side would equal . So both values of are impossible.
Thus , so and or . If , then we have the left side as . If , then we have as desired. Thus the only possibility for is .
Final answer
3