Question

a+b=3 a²+b²=19 a³+b³=??

Answer 1

Faz assim ...

(a + b)² = a² +2ab + b²

(a + b)² - (a² + b²) = 2ab

2ab = (a + b)² - (a² + b²)

ab = [(a + b)² - (a² + b²)]/2

ab = (3² - 19)/2

ab = -5

a³ + b³ = (a + b)(a² - ab + b²) = 3(19 + 5)

= 3(24)

= 72