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D( v )
4*v+20 = 0
v+5 = 0
4*v+20 = 0
4*v+20 = 0
4*v+20 = 0 // - 20
4*v = -20 // : 4
v = -20/4
v = -5
v+5 = 0
v+5 = 0
v+5 = 0 // - 5
v = -5
v in (-oo:-5) U (-5:+oo)
2-7/(4*v+20) = 7/(v+5) // - 7/(v+5)
2-7/(4*v+20)-(7/(v+5)) = 0
2-7/(4*v+20)-7*(v+5)^-1 = 0
2-7/(4*v+20)-7/(v+5) = 0
(-7*(v+5))/((4*v+20)*(v+5))+(-7*(4*v+20))/((4*v+20)*(v+5))+(2*(4*v+20)*(v+5))/((4*v+20)*(v+5)) = 0
2*(4*v+20)*(v+5)-7*(v+5)-7*(4*v+20) = 0
8*v^2-35*v+80*v-175+200 = 0
8*v^2+45*v+25 = 0
8*v^2+45*v+25 = 0
8*v^2+45*v+25 = 0
DELTA = 45^2-(4*8*25)
DELTA = 1225
DELTA > 0
v = (1225^(1/2)-45)/(2*8) or v = (-1225^(1/2)-45)/(2*8)
v = -5/8 or v = -5
(v+5)*(v+5/8) = 0
((v+5)*(v+5/8))/((4*v+20)*(v+5)) = 0
((v+5)*(v+5/8))/((4*v+20)*(v+5)) = 0 // * (4*v+20)*(v+5)
(v+5)*(v+5/8) = 0
( v+5/8 )
v+5/8 = 0 // - 5/8
v = -5/8
( v+5 )
v+5 = 0 // - 5
v = -5
v in { -5}
v = -5/8
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