Precalculus Examples

$f (7) = \sqrt{x - 21}$

Step 1

Replace the variable $x$ with $7$ in the expression.

$f (7) = \sqrt{(7) - 21}$

Step 2

Simplify the result.

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Step 2.1

Subtract $21$ from $7$ .

$f (7) = \sqrt{- 14}$

Step 2.2

Rewrite $- 14$ as $- 1 (14)$ .

$f (7) = \sqrt{- 1 \cdot 14}$

Step 2.3

Rewrite $\sqrt{- 1 (14)}$ as $\sqrt{- 1} \cdot \sqrt{14}$ .

$f (7) = \sqrt{- 1} \cdot \sqrt{14}$

Step 2.4

Rewrite $\sqrt{- 1}$ as $i$ .

$f (7) = i \sqrt{14}$

Step 2.5

The final answer is $i \sqrt{14}$ .

$i \sqrt{14}$

Step 3