If (a+b√3)^2=52+30√3, where a and b are natural numbers, then a+b equals
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Explanatory Answer
Question:
If (a + b√3)^2 = 52 + 30√3, where a and b are natural numbers, find a + b.
Solution:
Expand the left side:
(a + b√3)^2 = a^2 + 2ab√3 + 3b^2
Equate real and irrational parts with the right side 52 + 30√3:
Real part: a^2 + 3b^2 = 52
Irrational: 2ab = 30 ⇒ ab = 15
Find natural-number factor pairs of 15:
(ab = 15) ⇒ (a,b) ∈ {(1,15), (3,5), (5,3), (15,1)}
Check each pair against a^2 + 3b^2 = 52:
(1,15): 1^2 + 3·15^2 = 1 + 675 = 676 ≠ 52
(3,5): 3^2 + 3·5^2 = 9 + 75 = 84 ≠ 52
(5,3): 5^2 + 3·3^2 = 25 + 27 = 52 ✓
(15,1): 15^2 + 3·1^2 = 225 + 3 = 228 ≠ 52
Only (a,b) = (5,3) satisfies both equations.
Therefore:
a + b = 5 + 3 = 8
Answer: 8
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