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D( x )
x+6 = 0
x+6 = 0
x+6 = 0
x+6 = 0 // - 6
x = -6
x in (-oo:-6) U (-6:+oo)
(4*x^2+28*x+21)/(x+6) = 0
4*x^2+28*x+21 = 0
4*x^2+28*x+21 = 0
DELTA = 28^2-(4*4*21)
DELTA = 448
DELTA > 0
x = (448^(1/2)-28)/(2*4) or x = (-448^(1/2)-28)/(2*4)
x = (8*7^(1/2)-28)/8 or x = (-8*7^(1/2)-28)/8
(x-((-8*7^(1/2)-28)/8))*(x-((8*7^(1/2)-28)/8)) = 0
((x-((-8*7^(1/2)-28)/8))*(x-((8*7^(1/2)-28)/8)))/(x+6) = 0
( x-((-8*7^(1/2)-28)/8) )
x-((-8*7^(1/2)-28)/8) = 0 // + (-8*7^(1/2)-28)/8
x = (-8*7^(1/2)-28)/8
( x-((8*7^(1/2)-28)/8) )
x-((8*7^(1/2)-28)/8) = 0 // + (8*7^(1/2)-28)/8
x = (8*7^(1/2)-28)/8
x in { (-8*7^(1/2)-28)/8, (8*7^(1/2)-28)/8 }
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