WAEC 2020 · Paper 1 · Q33

The variables $x$ and $y$ are such that $y = 2x^3 - 2x^2 - 5x + 5$ . Calculate the corresponding change in $y$ when $x$ changes from 2.00 to 2.05.

Worked solution (try it first)

At $x = 2$ : $y = 16 - 8 - 10 + 5 = 3$ .
At $x = 2.05$ : $y = 2(8.615125) - 2(4.2025) - 10.25 + 5$
$= 3.57525$ .
The change is $3.57525 - 3 = 0.575$ , which is 0.58 to two decimal places, option A.