Find the Equation Given the Roots -3i , 8

$- 3 i$ , $8$

Step 1

Roots are the points where the graph intercepts with the x-axis $(y = 0)$ .

$y = 0$ at the roots

Step 2

The root at $x = - 3 i$ was found by solving for $x$ when $x - (- 3 i) = y$ and $y = 0$ .

The factor is $x + 3 i$

Step 3

The root at $x = 3 i$ was found by solving for $x$ when $x - (3 i) = y$ and $y = 0$ .

The factor is $x - 3 i$

Step 4

The root at $x = 8$ was found by solving for $x$ when $x - (8) = y$ and $y = 0$ .

The factor is $x - 8$

Step 5

Combine all the factors into a single equation.

$y = (x + 3 i) (x - 3 i) (x - 8)$

Step 6

Multiply all the factors to simplify the equation $y = (x + 3 i) (x - 3 i) (x - 8)$ .

Expand $(x + 3 i) (x - 3 i)$ using the FOIL Method.

Apply the distributive property.

$y = (x (x - 3 i) + 3 i (x - 3 i)) (x - 8)$

Apply the distributive property.

$y = (x \cdot x + x (- 3 i) + 3 i (x - 3 i)) (x - 8)$

Apply the distributive property.

$y = (x \cdot x + x (- 3 i) + 3 i x + 3 i (- 3 i)) (x - 8)$

Simplify terms.

Combine the opposite terms in $x \cdot x + x (- 3 i) + 3 i x + 3 i (- 3 i)$ .

Reorder the factors in the terms $x (- 3 i)$ and $3 i x$ .

$y = (x \cdot x - 3 i x + 3 i x + 3 i (- 3 i)) (x - 8)$

Add $- 3 i x$ and $3 i x$ .

$y = (x \cdot x + 0 + 3 i (- 3 i)) (x - 8)$

Add $x \cdot x$ and $0$ .

$y = (x \cdot x + 3 i (- 3 i)) (x - 8)$

Simplify each term.

Multiply $x$ by $x$ .

$y = (x^{2} + 3 i (- 3 i)) (x - 8)$

Multiply $3 i (- 3 i)$ .

Multiply $- 3$ by $3$ .

$y = (x^{2} - 9 i i) (x - 8)$

Raise $i$ to the power of $1$ .

$y = (x^{2} - 9 (i i)) (x - 8)$

Raise $i$ to the power of $1$ .

$y = (x^{2} - 9 (i i)) (x - 8)$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$y = (x^{2} - 9 i^{1 + 1}) (x - 8)$

Add $1$ and $1$ .

$y = (x^{2} - 9 i^{2}) (x - 8)$

Rewrite $i^{2}$ as $- 1$ .

$y = (x^{2} - 9 \cdot - 1) (x - 8)$

Multiply $- 9$ by $- 1$ .

$y = (x^{2} + 9) (x - 8)$

Expand $(x^{2} + 9) (x - 8)$ using the FOIL Method.

Apply the distributive property.

$y = x^{2} (x - 8) + 9 (x - 8)$

Apply the distributive property.

$y = x^{2} x + x^{2} \cdot - 8 + 9 (x - 8)$

Apply the distributive property.

$y = x^{2} x + x^{2} \cdot - 8 + 9 x + 9 \cdot - 8$

Simplify each term.

Multiply $x^{2}$ by $x$ by adding the exponents.

Multiply $x^{2}$ by $x$ .

Raise $x$ to the power of $1$ .

$y = x^{2} x + x^{2} \cdot - 8 + 9 x + 9 \cdot - 8$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$y = x^{2 + 1} + x^{2} \cdot - 8 + 9 x + 9 \cdot - 8$

Add $2$ and $1$ .

$y = x^{3} + x^{2} \cdot - 8 + 9 x + 9 \cdot - 8$

Move $- 8$ to the left of $x^{2}$ .

$y = x^{3} - 8 \cdot x^{2} + 9 x + 9 \cdot - 8$

Multiply $9$ by $- 8$ .

$y = x^{3} - 8 x^{2} + 9 x - 72$

Step 7

Find the Equation Given the Roots -3i , 8

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