Difficulty: Easy
Correct Answer: 161.3
Explanation:
Introduction / Context:The classic identity a^2 − b^2 = (a − b)(a + b) is a powerful shortcut, especially with decimals. It replaces squaring and subtracting with two additions/subtractions and one multiplication, greatly reducing error likelihood and saving time.
Given Data / Assumptions:
Concept / Approach:Apply a^2 − b^2 = (a − b)(a + b). The numbers are chosen so that a − b is an integer, making the product particularly simple to evaluate accurately.
Step-by-Step Solution:
a − b = 13.065 − 3.065 = 10.000.a + b = 13.065 + 3.065 = 16.130.Therefore a^2 − b^2 = (a − b)(a + b) = 10.000 × 16.130 = 161.3.Verification / Alternative check:
Rough check: 13^2 − 3^2 = 169 − 9 = 160, near 161.3, consistent with decimal offsets.Why Other Options Are Wrong:
Common Pitfalls:
Final Answer:
161.3
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