Question

1 If x + 1/x = 7, then the value of x^3 +1/x^3 is :
​

Answer 1

Answer:

Solution

Given:

x+1x

=7

Cubing both the sides, we get,

⇒

(x+1x)3

=73

⇒

x3+1x3+3(x)(1x)(x+1x)

=

343

⇒

x3+1x3+3(7)

=343

⇒x3+1×3

=343−21

-x3+1x3

=322

Answer 2

Given

x+(1/x) = 7

cubing on both sides:

=>(x+1/x)³ = 7³

=> x³+(1/x³)+3(x)(1/x)(x+1/x)=343

=> x³+1/x³+3(7) =343

=> x³+1/x³ = 343-21

:. x³+1/x³ = 322