Question

If 3x - `4/x` = 4; and x ≠ 0 find : 27x³ - `64/x^3`

Answer 1

3x - `4/x` = 4;

We need to find 27x³ - `64/x^3`

Let us now consider the expansion of `( 3x - 4/x )^3` :
`( 3x - 4/x )^3 = 27x^3 - 64/x^3 - 3 xx 3x xx 4/x( 3x - 4/x )`

⇒ `(4)^3 = 27x^3 - 64/x^3 - 144         ["Given :" 3x - 4/x = 4]`

⇒ 64 + 144 = 27x³ - `64/x^3`

⇒ 27x3 - `64/x^3` = 208