If a + b are two positive real numbers such that a + b = 20 and ab = 4, then the value of $a^3 + b^3$ is :
Answer & explanation
Correct answer: option 1
If x + y = n
then, $x^3 + y^3$ = n3 - 3 × n × xy
a + b = 20
ab = 4,
then the value of $a^3 + b^3$ = 203 - 3 × 20 × 4
$a^3 + b^3$ = 8000 - 240 = 7760