SOLUTION: What two numbers multiplies to -8000 but add to +20?

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Question 1023773: What two numbers multiplies to -8000 but add to +20?
Found 2 solutions by Fombitz, msalonga:
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Use Cramer's rule,
A=%28matrix%283%2C3%2C%0D%0A2%2C-3%2C-2%2C%0D%0A3%2C-4%2C3%2C%0D%0A4%2C-5%2C4%0D%0A%29%29
abs%28A%29=-4
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abs%28A%5Bx%5D%29=-4
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abs%28A%5By%5D%29=8
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.
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abs%28A%5Bz%5D%29=4
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x=abs%28A%5Bx%5D%29%2Fabs%28A%29=%28-4%29%2F%28-4%29=1
y=abs%28A%5By%5D%29%2Fabs%28A%29=%288%29%2F%28-4%29=-2
z=abs%28A%5Bz%5D%29%2Fabs%28A%29=%284%29%2F%28-4%29=-1

Answer by msalonga(4) About Me  (Show Source):
You can put this solution on YOUR website!
eq 1. xy = -8000
eq 2. x+y = 20
from eq 2. y = 20 - x
substituting y to eq. 2
x(20-x) = -8000
20x - x^2 = -8000, rearraging to ax^2 + bx + c = 0
x^2 - 20x - 8000 = 0; a = 1; b = -20; c = -8000
using quadratic formula
x = 100 and -80