Question

Find$f\left(3\right)$if$f\left(x\right)=-4x^2+5x$.

Short answer

The value of$f\left(3\right)=-21$.

Step-by-step solution

Step 1. Given Information

The given function is :

$f\left(x\right)=-4x^2+5x$

Step 2. Substitute the value of x=3.

The value of $f\left(3\right)$is

$\begin{array}{rcl}f\left(3\right)& =& -4\times 3^2+5\times 3\\ f\left(3\right)& =& -4\times 9+15\\ f\left(3\right)& =& -36+15\\ f\left(3\right)& =& -21\end{array}$