If $a^3+b^3=405$ and a + b = 9, then the value of ab is
Answer & explanation
Correct answer: option 4
a3 + b3 = 405
a + b = 9
(a + b)3 = a3 + b3 + 3ab(a + b)
= (9)3 = 405 + 3ab (9)
= 729 = 405 + 27ab
= 27ab = 324
= ab = 12
If $a^3+b^3=405$ and a + b = 9, then the value of ab is
Correct answer: option 4
a3 + b3 = 405
a + b = 9
(a + b)3 = a3 + b3 + 3ab(a + b)
= (9)3 = 405 + 3ab (9)
= 729 = 405 + 27ab
= 27ab = 324
= ab = 12