Given:

We solve the above equation by using the formula

(a + b)³ = a³ + b³ + 3a²b + 3ab²

[∵ i² = -1]

Now, we rationalize the above by multiplying and divide by the conjugate of 3 + i

…(i)

Now, we know that,

(a + b)(a – b) = (a² – b²)

So, eq. (i) become

[∵ i² = -1]

[∵ i² = -1]