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  4. If f(x) = 2-2x2, find (f(3,8)-f(4) /3.8-4) ,

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

KCETKCET 2015Relations and Functions

Solution:

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