panda557 panda557

03-06-2016
Mathematics

contestada

What is x^2+x-20=0.
please help

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meerkat18 meerkat18

03-06-2016

x² + x - 20 = 0

x² = x * x
x = the sum of the factors of -20
-20 ⇒ 1 x 20
2 x 10
- 4 x 5 ⇒ only these factors can arrive to a sum of 1

(x - 4)(x + 5) = x(x+5) - 4(x+5) = x² + 5x - 4x - 20 = x² + x - 20

x - 4 = 0
x = 4

x + 5 = 0
x = -5

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