Cho \(f\left( x \right) = 5{x^2} - 16\sqrt x + 7\). Tính \(f'\left( 4 \right);f'\left( {\frac{1}{4}} \right)\)
\(f'\left( x \right) = 10x - 16.\frac{1}{{2\sqrt x }} = 10x - \frac{8}{{\sqrt x }}\)
Suy ra
\(\begin{array}{l}
f'\left( 4 \right) = 10.4 - \frac{8}{{\sqrt 4 }} = 50 - 4 = 36\\
f'\left( {\frac{1}{4}} \right) = 10.\frac{1}{4} - \frac{8}{{\sqrt {\frac{1}{4}} }} = - \frac{{27}}{2}
\end{array}\)
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