Question

x+y=5,xy=18 ,then x3 +y3 =?
​

Answer 1

Answer:

875

Step-by-step explanation:

x+y=5 xy=18

(x+y)²=x²+2xy+y²

5²=  x² + (2 × 18) +y²

25 = x² + 36 + y²

25 - 36 = x² + y²

-11 = x² + y²

x³ + y³ = (x+y)³ (x²+xy+y²)

=(5)³ (x²+18+y²)

=125 × (x²+y²+18)

=125 × (-11+18)

=125 × 7

=875