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Number theory Difficulty 6.0 AIME, harder Find the answer

Find the sum of all values of a+ba + b, where (a,b)(a, b) is an ordered pair of positive integers and a2+2017b2a^2+\sqrt{2017-b^2} is a perfect square.

A number or a short expression. Spacing and $ signs are ignored.

Solution

1. We start with the equation a2+2017b2=k2a^2 + \sqrt{2017 - b^2} = k^2 where kk is an integer. For this to be true, 2017b2\sqrt{2017 - b^2} must also be an integer. Let 2017b2=m\sqrt{2017 - b^2} = m where mm is an integer. Therefore, we have:
2017b2=m2 2017 - b^2 = m^2
This can be rewritten as:
2017=b2+m2 2017 = b^2 + m^2
This implies that b2+m2=2017b^2 + m^2 = 2017.

2. We need to find pairs (b,m)(b, m) such that both bb and mm are integers. We test values of bb to find corresponding mm values that satisfy the equation.

3. Testing b=44b = 44:
2017442=20171936=81 2017 - 44^2 = 2017 - 1936 = 81
81=9 \sqrt{81} = 9
So, one pair is (b,m)=(44,9)(b, m) = (44, 9).

4. Testing b=9b = 9:
201792=201781=1936 2017 - 9^2 = 2017 - 81 = 1936
1936=44 \sqrt{1936} = 44
So, another pair is (b,m)=(9,44)(b, m) = (9, 44).

5. Now, we have two pairs (b,m)(b, m): (44,9)(44, 9) and (9,44)(9, 44). We need to find corresponding aa values such that a2+m=k2a^2 + m = k^2.

6. For (b,m)=(44,9)(b, m) = (44, 9):
a2+9=k2 a^2 + 9 = k^2
This can be rewritten as:
k2a2=9 k^2 - a^2 = 9
(ka)(k+a)=9 (k - a)(k + a) = 9
The factor pairs of 9 are (1,9)(1, 9) and (3,3)(3, 3). Solving these:
- For (1,9)(1, 9):
ka=1andk+a=9 k - a = 1 \quad \text{and} \quad k + a = 9
Adding these equations:
2k=10    k=5 2k = 10 \implies k = 5
Subtracting these equations:
2a=8    a=4 2a = 8 \implies a = 4
So, one solution is (a,b)=(4,44)(a, b) = (4, 44).

7. For (b,m)=(9,44)(b, m) = (9, 44):
a2+44=k2 a^2 + 44 = k^2
This can be rewritten as:
k2a2=44 k^2 - a^2 = 44
(ka)(k+a)=44 (k - a)(k + a) = 44
The factor pairs of 44 are (1,44)(1, 44), (2,22)(2, 22), and (4,11)(4, 11). Solving these:
- For (2,22)(2, 22):
ka=2andk+a=22 k - a = 2 \quad \text{and} \quad k + a = 22
Adding these equations:
2k=24    k=12 2k = 24 \implies k = 12
Subtracting these equations:
2a=20    a=10 2a = 20 \implies a = 10
So, another solution is (a,b)=(10,9)(a, b) = (10, 9).

8. The solutions (a,b)(a, b) are (4,44)(4, 44) and (10,9)(10, 9). The sums a+ba + b are:
4+44=48 4 + 44 = 48
10+9=19 10 + 9 = 19
Therefore, the total sum is:
48+19=67 48 + 19 = 67

The final answer is 67\boxed{67}

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.