The sum of squares of two numbers is 68, and the square of their difference is 36. Find the product of the two numbers.

Difficulty: Easy

Correct Answer: 16

Explanation:


Introduction / Context:
This question leverages the identity for the square of a difference and its relationship to the product term. With aggregate information (sum of squares and squared difference), we can deduce the product directly without solving for individual numbers.


Given Data / Assumptions:

  • a^2 + b^2 = 68.
  • (a − b)^2 = 36.
  • We need ab.


Concept / Approach:
Use the identity (a − b)^2 = a^2 + b^2 − 2ab. Plug in the given values and solve for ab. This bypasses solving a quadratic for a and b and goes straight to the required product.


Step-by-Step Solution:

Start: (a − b)^2 = a^2 + b^2 − 2ab.Substitute: 36 = 68 − 2ab.Rearrange: 2ab = 68 − 36 = 32.Therefore, ab = 32 / 2 = 16.


Verification / Alternative check:
Optional: (a + b)^2 = a^2 + b^2 + 2ab = 68 + 32 = 100 → a + b = 10 is consistent with real solutions (e.g., numbers satisfying sum 10 and product 16 exist).


Why Other Options Are Wrong:
32 represents 2ab, not ab. 58 and 104 are inconsistent with the identity. 22 is arbitrary here.


Common Pitfalls:
Forgetting to divide by 2 after finding 2ab, or mixing identities for (a − b)^2 and (a + b)^2.


Final Answer:
16

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