If a³ + b³ = 280 and a + b = 10, find ab.
Show answer & explanation
Correct answer: A
Explanation
Given:
a + b = 10, a³ + b³ = 280
Formula:
a³ + b³ = (a + b)³ − 3ab(a + b)
280 = 10³ − 3ab × 10
280 = 1000 − 30ab
30ab = 1000 − 280 = 720
ab = 720 / 30 = 24