Find the value of a^3 - b^3, when a - b = 4 and ab = 5?
- 118
- 128
- 124
- None of these
Explanation
Given:
a - b = 4
ab = 5
The formula for a³ - b³ is:
a³ - b³ = (a - b)(a² + ab + b²)
We can also use the identity:
a³ - b³ = (a - b)³ + 3ab(a - b)
Substituting the given values:
a³ - b³ = (4)³ + 3 * 5 * 4
= 64 + 60
= 124
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