Question

What two numbers multiply to -20 then add to -8?

Answer 1

Answer: 2 and -10

Explanation:

Starter:

Let x be one of the two numbers

Let y be the other number

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Solve:

Given

x + y = -8

xy = -20

Simplify

x = -8 - y

xy = -20

Substitution

(-8 - y)y = -20

Expand parenthesis

-8y - y² = -20

Add 20 on both sides

-8y - y² + 20 = -20 + 20

-8y - y² + 20 = 0

Solve quadratic equation

(y - 2) (y + 10) = 0

y = 2 or y = -10

x = -8 - y

x = -8 - (2) or x = -8 - (10)

x = -10 or x = 2

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Answer 2

-10 and 2

Explanation:

1. Think about what numbers multiply to -20: -10 and 2, 10 and -2, -20 and 1, 20 and -1, 4 and -5, -4 and 5

2. Then, think about which of the above adds to -8. This leaves you with -10 and 2