Use the (a − b)^3 pattern to simplify Evaluate (.58)^3 − (.42)^3 − 3 * (.58) * (.42) * (.58 − .42) exactly.

Difficulty: Easy

Correct Answer: 0.004096

Explanation:


Introduction / Context:
This expression is designed for the binomial cube identity. Recognizing the structure a^3 − b^3 − 3ab(a − b) allows immediate simplification to (a − b)^3, which is simple to compute.



Given Data / Assumptions:

  • a = 0.58, b = 0.42.
  • Expression: a^3 − b^3 − 3ab(a − b).
  • a − b = 0.16.


Concept / Approach:
Identity: (a − b)^3 = a^3 − b^3 − 3ab(a − b). Hence the entire expression equals (a − b)^3. This avoids tedious cubic computations.



Step-by-Step Solution:
Compute a − b = 0.58 − 0.42 = 0.16.By identity, value = (a − b)^3 = (0.16)^3.0.16^2 = 0.0256; multiply by 0.16: 0.0256 * 0.16 = 0.004096.



Verification / Alternative check:
Expanding (0.16)^3 directly or evaluating a^3, b^3, and 3ab(a − b) numerically will agree with 0.004096.



Why Other Options Are Wrong:
1.3976 and 1 are far too large; 0.16 is (a − b), not its cube; 0.04096 is off by a factor of 10.



Common Pitfalls:
Forgetting the exact identity; cubing only the difference once; decimal place errors when cubing small decimals.



Final Answer:
0.004096


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