Question

if x=1/5-x find x^3+1/x^3

Answer 1

Given , x = 1/5 - x

=> 2x = 1/5

=> x = 1/10 and 1/x = 10

( x + 1/x) ³ = x³ + 1/x ³ + 2 ( x + 1/x)

(1/10 + 10)³ = x³ + 1/x ³ + 2 ( 1/10 + 10)

(101/10)³ = x³ + 1/x ³ + 2 × 101/10

1030301/ 1000 = x³ + 1/x³ + 101/5

x³ + 1/x³ = 1010101/ 1000

Ans.= 1010.101

Answer 2

Given: x = 5-1/x => x +1/x =5

Required: x^3+1/x^3

Solution: x^3+1/x^3 = (x+1/x)^3-3(x+1/x)

= (5)^3-3*5

= 125-15

= 110 Ans.