Question:
If $g(x)=x^{2}+x-1$ and
$(g \circ f)(x)=4 x^{2}-10 x+5$, then $f\left(\frac{5}{4}\right)$ is equal to
Correct Option: , 2
Solution:
$g(x)=x^{2}+x-1$
$g(f(x))=4 x^{2}-10 x+5$
$=(2 x-2)^{2}+(2-2 x)-1$
$=(2-2 x)^{2}+(2-2 x)-1$
$\Rightarrow f(x)=2-2 x$
$f\left(\frac{5}{4}\right)=\frac{-1}{2}$
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