Question

if : a is not equal to 0 and a-1/a=4; find: a³-1/a³​

Answer 1

Answer:

(a-1)/a=4

a-1=4a

or

a=-1/3

so

(a³-1)/a³=((-1/3)³-1)/(-1/3)³

=)(-1-27)/27÷-1/27

=)28

Answer 2

Answer:

76

Step-by-step explanation:

a - 1/a = 4 ...(1)

Cube on both sides :

=> (a - 1/a)³ = 4³

=> (a)³ - (1/a)³ - 3(a)(1/a)(a - 1/a) = 64

=> a³ - 1/a³ - 3(a × 1/a)(a - 1/a) = 64

=> a³ - 1/a³ - 3(1)(4) = 64 {from (1)}

=> a³ - 1/a³ - 12 = 64

=> a³ - 1/a³ = 76

Using (x - y)³ = x³ - y³ - 3xy(x - y)