Find the Maximum/Minimum Value f(x)=x^2-9x

$f (x) = x^{2} - 9 x$

Step 1

The minimum of a quadratic function occurs at $x = - \frac{b}{2 a}$ . If $a$ is positive, the minimum value of the function is $f (- \frac{b}{2 a})$ .

$f_{min}$ $x = a x^{2} + b x + c$ occurs at $x = - \frac{b}{2 a}$

Step 2

Find the value of $x = - \frac{b}{2 a}$ .

Substitute in the values of $a$ and $b$ .

$x = - \frac{- 9}{2 (1)}$

Remove parentheses.

$x = - \frac{- 9}{2 (1)}$

Simplify $- \frac{- 9}{2 (1)}$ .

Multiply $2$ by $1$ .

$x = - \frac{- 9}{2}$

Move the negative in front of the fraction.

$x = - - \frac{9}{2}$

Multiply $- - \frac{9}{2}$ .

Multiply $- 1$ by $- 1$ .

$x = 1 (\frac{9}{2})$

Multiply $\frac{9}{2}$ by $1$ .

$x = \frac{9}{2}$

Step 3

Evaluate $f (\frac{9}{2})$ .

Replace the variable $x$ with $\frac{9}{2}$ in the expression.

$f (\frac{9}{2}) = {(\frac{9}{2})}^{2} - 9 (\frac{9}{2})$

Simplify the result.

Simplify each term.

Apply the product rule to $\frac{9}{2}$ .

$f (\frac{9}{2}) = \frac{9^{2}}{2^{2}} - 9 (\frac{9}{2})$

Raise $9$ to the power of $2$ .

$f (\frac{9}{2}) = \frac{81}{2^{2}} - 9 (\frac{9}{2})$

Raise $2$ to the power of $2$ .

$f (\frac{9}{2}) = \frac{81}{4} - 9 (\frac{9}{2})$

Multiply $- 9 (\frac{9}{2})$ .

Combine $- 9$ and $\frac{9}{2}$ .

$f (\frac{9}{2}) = \frac{81}{4} + \frac{- 9 \cdot 9}{2}$

Multiply $- 9$ by $9$ .

$f (\frac{9}{2}) = \frac{81}{4} + \frac{- 81}{2}$

Move the negative in front of the fraction.

$f (\frac{9}{2}) = \frac{81}{4} - \frac{81}{2}$

To write $- \frac{81}{2}$ as a fraction with a common denominator, multiply by $\frac{2}{2}$ .

$f (\frac{9}{2}) = \frac{81}{4} - \frac{81}{2} \cdot \frac{2}{2}$

Write each expression with a common denominator of $4$ , by multiplying each by an appropriate factor of $1$ .

Multiply $\frac{81}{2}$ by $\frac{2}{2}$ .

$f (\frac{9}{2}) = \frac{81}{4} - \frac{81 \cdot 2}{2 \cdot 2}$

Multiply $2$ by $2$ .

$f (\frac{9}{2}) = \frac{81}{4} - \frac{81 \cdot 2}{4}$

Combine the numerators over the common denominator.

$f (\frac{9}{2}) = \frac{81 - 81 \cdot 2}{4}$

Simplify the numerator.

Multiply $- 81$ by $2$ .

$f (\frac{9}{2}) = \frac{81 - 162}{4}$

Subtract $162$ from $81$ .

$f (\frac{9}{2}) = \frac{- 81}{4}$

Move the negative in front of the fraction.

$f (\frac{9}{2}) = - \frac{81}{4}$

The final answer is $- \frac{81}{4}$ .

$- \frac{81}{4}$

Step 4

Use the $x$ and $y$ values to find where the minimum occurs.

$(\frac{9}{2}, - \frac{81}{4})$

Step 5

Find the Maximum/Minimum Value f(x)=x^2-9x

Related Questions

Support LCMGCF.com by disabling your adblocker.