Use (a^2 − b^2) = (a − b)(a + b): The difference of the squares of two numbers is 256000 and their sum is 1000. Find the two numbers.
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A600, 400
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B628, 372
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C640, 360
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DNone of these
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E700, 300
Answer
Correct Answer: 628, 372
Explanation
Introduction / Context:This problem is a direct application of the identity a^2 − b^2 = (a − b)(a + b). With the sum given, the difference of the squares quickly yields the difference of the numbers, from which the pair is recovered uniquely (assuming a ≥ b).
Given Data / Assumptions:
- a^2 − b^2 = 256000
- a + b = 1000
- We look for real numbers a ≥ b; integers are suggested by the data.
Concept / Approach:Factor the square difference: (a − b)(a + b) = 256000. Since a + b = 1000, it follows that a − b = 256000 / 1000 = 256. Solve the simultaneous equations for a and b.
Step-by-Step Solution:a + b = 1000a − b = 256Add to get a: 2a = 1256 → a = 628Then b = 1000 − 628 = 372
Verification / Alternative check:Compute a^2 − b^2 = (a − b)(a + b) = 256 * 1000 = 256000, which matches exactly.
Why Other Options Are Wrong:600,400 gives (a − b) = 200, not 256; 640,360 gives (a − b) = 280; the others do not satisfy both the sum and square-difference conditions.
Common Pitfalls:Confusing a^2 − b^2 with (a − b)^2. The correct identity uses the product (a − b)(a + b).
Final Answer:628, 372