alexzigg99 alexzigg99

25-04-2017
Mathematics

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solve for x x2+4x-21=0

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mohabbasem mohabbasem

25-04-2017

First you calculate the determinant:
d=b^2-4ac
d=4^2-4*1*(-21)=16+84=100

Because d>0 there are two solutions for x:

x_1 = (-b+√d)/2a = (-4+√100)/2*1 = 6/2 = 3
x_2 = (-b-√d)/2a = (-4-√100)/2*1 = -14/2 =-7

The solutions for x is x = 3 and x = -7

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