Use differentials to find an approximate value for

: Let y = f(x) =  x^1/3  
Then dy = 1/3*x^(−2/3) dx 
 Since f(64) = 4.
We take x = 64 and dx = ∆x = 1  
This gives dy = 1/3*(64)^(−2/3)* (1) =  1/48  
∴65^(1/3) = f(64 + 1) ≈ f(64) + dy = 4 + 1/48 ≈ 4.021