(i) x3 - 16
Let y = x3 – 16
Again, let y + δy = (x + δx)3 – 16
⇒ δy = (x + δx)3 – 16 – y
⇒ δy = (x + δx)3 – 16 – x3 + 16
⇒ δy = (x + δx)3 – x3
(ii) (x - 1)(x - 2)
Let y = (x – 1) (x – 2) = x2 – 3x + 2
Again, let y + δy = (x + δx)2 – 3(x + δx) + 2
⇒ δy = (x + δx)2 – 3(x + δx) + 2 – x2 + 3x – 2
(iii) 1/x2
(iv) (x + 1)/(x - 1)