Mathematics - Application of Derivative Question with Solution | TestHub

Given, $A=\left\{x\mid x^2+20\le 9x\right\}$ $=\{x\mid x\in [4,5]\}$ Now, $f^{\prime }(x)=6\left(x^2-5x+6\right)$ Put $f^{\prime }(x)=0\Rightarrow x=2,3$ $f(2)=-20,f(3)=-21$, $f(4)=-16,f(5)=7$
From graph, maximum of $f(x)$ on set $A$ is $f(5)=7$.