Find the Equation Given the Roots -1 , 3i

$- 1$ , $3 i$

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 $x = - 1$ was found by solving for $x$ when $x - (- 1) = y$ and $y = 0$ .

The factor is $x + 1$

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

The factor is $x + 3 i$

Step 5

Combine all the factors into a single equation.

$y = (x + 1) (x - 3 i) (x + 3 i)$

Step 6

Multiply all the factors to simplify the equation $y = (x + 1) (x - 3 i) (x + 3 i)$ .

Expand $(x + 1) (x - 3 i)$ using the FOIL Method.

Apply the distributive property.

$y = (x (x - 3 i) + 1 (x - 3 i)) (x + 3 i)$

Apply the distributive property.

$y = (x \cdot x + x (- 3 i) + 1 (x - 3 i)) (x + 3 i)$

Apply the distributive property.

$y = (x \cdot x + x (- 3 i) + 1 x + 1 (- 3 i)) (x + 3 i)$

Simplify each term.

Multiply $x$ by $x$ .

$y = (x^{2} + x (- 3 i) + 1 x + 1 (- 3 i)) (x + 3 i)$

Multiply $x$ by $1$ .

$y = (x^{2} + x (- 3 i) + x + 1 (- 3 i)) (x + 3 i)$

Multiply $- 3 i$ by $1$ .

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

Expand $(x^{2} + x (- 3 i) + x - 3 i) (x + 3 i)$ by multiplying each term in the first expression by each term in the second expression.

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

Simplify terms.

Combine the opposite terms in $x^{2} x + x^{2} (3 i) + x (- 3 i) x + x (- 3 i) (3 i) + x \cdot x + x (3 i) - 3 i x - 3 i (3 i)$ .

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

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

Subtract $3 i x$ from $3 i x$ .

$y = x^{2} x + x^{2} (3 i) + x (- 3 i) x + x (- 3 i) (3 i) + x \cdot x + 0 - 3 i (3 i)$

Add $x^{2} x + x^{2} (3 i) + x (- 3 i) x + x (- 3 i) (3 i) + x \cdot x$ and $0$ .

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

Simplify each term.

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

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

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

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

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

$y = x^{2 + 1} + x^{2} (3 i) + x (- 3 i) x + x (- 3 i) (3 i) + x \cdot x - 3 i (3 i)$

Add $2$ and $1$ .

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

Move $3$ to the left of $x^{2}$ .

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

Multiply $x$ by $x$ by adding the exponents.

Move $x$ .

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

Multiply $x$ by $x$ .

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

Multiply $x (- 3 i) (3 i)$ .

Multiply $3$ by $- 3$ .

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + x (- 9 i) i + x \cdot x - 3 i (3 i)$

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

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + x (- 9 (i i)) + x \cdot x - 3 i (3 i)$

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

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + x (- 9 (i i)) + x \cdot x - 3 i (3 i)$

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

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + x (- 9 i^{1 + 1}) + x \cdot x - 3 i (3 i)$

Add $1$ and $1$ .

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + x (- 9 i^{2}) + x \cdot x - 3 i (3 i)$

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

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + x (- 9 \cdot - 1) + x \cdot x - 3 i (3 i)$

Multiply $- 9$ by $- 1$ .

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + x \cdot 9 + x \cdot x - 3 i (3 i)$

Move $9$ to the left of $x$ .

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 \cdot x + x \cdot x - 3 i (3 i)$

Multiply $x$ by $x$ .

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 x + x^{2} - 3 i (3 i)$

Multiply $- 3 i (3 i)$ .

Multiply $3$ by $- 3$ .

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 x + x^{2} - 9 i i$

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

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 x + x^{2} - 9 (i i)$

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

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 x + x^{2} - 9 (i i)$

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

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 x + x^{2} - 9 i^{1 + 1}$

Add $1$ and $1$ .

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 x + x^{2} - 9 i^{2}$

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

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 x + x^{2} - 9 \cdot - 1$

Multiply $- 9$ by $- 1$ .

$y = x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 x + x^{2} + 9$

Simplify by adding terms.

Combine the opposite terms in $x^{3} + 3 x^{2} i + x^{2} (- 3 i) + 9 x + x^{2} + 9$ .

Reorder the factors in the terms $3 x^{2} i$ and $x^{2} (- 3 i)$ .

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

Subtract $3 i x^{2}$ from $3 i x^{2}$ .

$y = x^{3} + 0 + 9 x + x^{2} + 9$

Add $x^{3}$ and $0$ .

$y = x^{3} + 9 x + x^{2} + 9$

Move $9 x$ .

$y = x^{3} + x^{2} + 9 x + 9$

Step 7

Find the Equation Given the Roots -1 , 3i

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