Precalculus Examples

$f (x) = - 3 x^{2} + 9 x - 8$ Find $f (5)$

Step 1

Replace the variable $x$ with $5$ in the expression.

$f (5) = - 3 {(5)}^{2} + 9 (5) - 8$

Step 2

Simplify $- 3 {(5)}^{2} + 9 (5) - 8$ .

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Step 2.1

Remove parentheses.

$- 3 {(5)}^{2} + 9 (5) - 8$

Step 2.2

Simplify each term.

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Step 2.2.1

Raise $5$ to the power of $2$ .

$- 3 \cdot 25 + 9 (5) - 8$

Step 2.2.2

Multiply $- 3$ by $25$ .

$- 75 + 9 (5) - 8$

Step 2.2.3

Multiply $9$ by $5$ .

$- 75 + 45 - 8$

Step 2.3

Simplify by adding and subtracting.

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Step 2.3.1

Add $- 75$ and $45$ .

$- 30 - 8$

Step 2.3.2

Subtract $8$ from $- 30$ .

$- 38$