Find the Equation Given the Roots 5 , 2i , -2i

$5$ , $2 i$ , $- 2 i$

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 $x = 5$ was found by solving for $x$ when $x - (5) = y$ and $y = 0$ .

The factor is $x - 5$

Step 3

The root at $x = 2 i$ was found by solving for $x$ when $x - (2 i) = y$ and $y = 0$ .

The factor is $x - 2 i$

Step 4

The root at $x = - 2 i$ was found by solving for $x$ when $x - (- 2 i) = y$ and $y = 0$ .

The factor is $x + 2 i$

Step 5

Combine all the factors into a single equation.

$y = (x - 5) (x - 2 i) (x + 2 i)$

Step 6

Multiply all the factors to simplify the equation $y = (x - 5) (x - 2 i) (x + 2 i)$ .

Expand $(x - 5) (x - 2 i)$ using the FOIL Method.

Apply the distributive property.

$y = (x (x - 2 i) - 5 (x - 2 i)) (x + 2 i)$

Apply the distributive property.

$y = (x \cdot x + x (- 2 i) - 5 (x - 2 i)) (x + 2 i)$

Apply the distributive property.

$y = (x \cdot x + x (- 2 i) - 5 x - 5 (- 2 i)) (x + 2 i)$

Simplify each term.

Multiply $x$ by $x$ .

$y = (x^{2} + x (- 2 i) - 5 x - 5 (- 2 i)) (x + 2 i)$

Multiply $- 2$ by $- 5$ .

$y = (x^{2} + x (- 2 i) - 5 x + 10 i) (x + 2 i)$

Expand $(x^{2} + x (- 2 i) - 5 x + 10 i) (x + 2 i)$ by multiplying each term in the first expression by each term in the second expression.

$y = x^{2} x + x^{2} (2 i) + x (- 2 i) x + x (- 2 i) (2 i) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

Simplify terms.

Simplify each term.

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

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

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

$y = x^{2} x + x^{2} (2 i) + x (- 2 i) x + x (- 2 i) (2 i) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

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

$y = x^{2 + 1} + x^{2} (2 i) + x (- 2 i) x + x (- 2 i) (2 i) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

Add $2$ and $1$ .

$y = x^{3} + x^{2} (2 i) + x (- 2 i) x + x (- 2 i) (2 i) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

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

$y = x^{3} + 2 \cdot (x^{2} i) + x (- 2 i) x + x (- 2 i) (2 i) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

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

Move $x$ .

$y = x^{3} + 2 x^{2} i + x \cdot x (- 2 i) + x (- 2 i) (2 i) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

Multiply $x$ by $x$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + x (- 2 i) (2 i) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

Multiply $x (- 2 i) (2 i)$ .

Multiply $2$ by $- 2$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + x (- 4 i) i - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

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

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + x (- 4 (i i)) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

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

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + x (- 4 (i i)) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

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

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + x (- 4 i^{1 + 1}) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

Add $1$ and $1$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + x (- 4 i^{2}) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

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

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + x (- 4 \cdot - 1) - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

Multiply $- 4$ by $- 1$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + x \cdot 4 - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

Move $4$ to the left of $x$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 \cdot x - 5 x \cdot x - 5 x (2 i) + 10 i x + 10 i (2 i)$

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

Move $x$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 (x \cdot x) - 5 x (2 i) + 10 i x + 10 i (2 i)$

Multiply $x$ by $x$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 5 x (2 i) + 10 i x + 10 i (2 i)$

Multiply $2$ by $- 5$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 10 x i + 10 i x + 10 i (2 i)$

Multiply $10 i (2 i)$ .

Multiply $2$ by $10$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 10 x i + 10 i x + 20 i i$

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

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 10 x i + 10 i x + 20 (i i)$

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

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 10 x i + 10 i x + 20 (i i)$

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

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 10 x i + 10 i x + 20 i^{1 + 1}$

Add $1$ and $1$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 10 x i + 10 i x + 20 i^{2}$

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

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 10 x i + 10 i x + 20 \cdot - 1$

Multiply $20$ by $- 1$ .

$y = x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 10 x i + 10 i x - 20$

Simplify by adding terms.

Combine the opposite terms in $x^{3} + 2 x^{2} i + x^{2} (- 2 i) + 4 x - 5 x^{2} - 10 x i + 10 i x - 20$ .

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

$y = x^{3} + 2 i x^{2} - 2 i x^{2} + 4 x - 5 x^{2} - 10 x i + 10 i x - 20$

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

$y = x^{3} + 0 + 4 x - 5 x^{2} - 10 x i + 10 i x - 20$

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

$y = x^{3} + 4 x - 5 x^{2} - 10 x i + 10 i x - 20$

Reorder the factors in the terms $- 10 x i$ and $10 i x$ .

$y = x^{3} + 4 x - 5 x^{2} - 10 i x + 10 i x - 20$

Add $- 10 i x$ and $10 i x$ .

$y = x^{3} + 4 x - 5 x^{2} + 0 - 20$

Add $x^{3} + 4 x - 5 x^{2}$ and $0$ .

$y = x^{3} + 4 x - 5 x^{2} - 20$

Move $4 x$ .

$y = x^{3} - 5 x^{2} + 4 x - 20$

Step 7

Find the Equation Given the Roots 5 , 2i , -2i

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