Question

If $f(x) = 2-2x^2,$ find $\frac {f(3,8)-f(4)} {3.8-4}$,

• A. 1.56
• B. 156
• C. 15.6
• D. 0.156

Answer 1

Answer: (C)

15.6

Answer 2

We have, $f\left(x\right) = 2x^{2}$
$\therefore\, \frac{f\left(3.8\right)-f\left(4\right)}{3.8-4}=\frac{2\left(3.8 \right)^{2}-2\left(4\right)^{2}}{3.8-4}$
$=\frac{2\left[\left(3.8\right)^{2}-\left(4\right)^{2}\right]}{3.8-4}$
$\quad \quad \quad =\frac{2\left(3.8-4\right)\left(3.8+4\right)}{3.8}=2\left(7.8\right)=15.6$