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D( y )
y = 0
y = 0
y = 0
y in (-oo:0) U (0:+oo)
(1/y)*(7/y-1) = 9/8 // - 9/8
(1/y)*(7/y-1)-(9/8) = 0
(1/y)*(7/y-1)-9/8 = 0
y^-1*(7*y^-1-1)-9/8 = 0
(8*y^-1*(7*y^-1-1))/8-9/8 = 0
8*y^-1*(7*y^-1-1)-9 = 0
56*y^-2-8*y^-1-9 = 0
56*y^-2-8*y^-1-9 = 0
56*y^-2-8*y^-1-9*y^0 = 0
(56*y^0-9*y^2-8*y^1)/(y^2) = 0 // * y^4
y^2*(56*y^0-9*y^2-8*y^1) = 0
y^2
56-9*y^2-8*y = 0
56-9*y^2-8*y = 0
DELTA = (-8)^2-(-9*4*56)
DELTA = 2080
DELTA > 0
y = (2080^(1/2)+8)/(-9*2) or y = (8-2080^(1/2))/(-9*2)
y = (4*130^(1/2)+8)/(-18) or y = (8-4*130^(1/2))/(-18)
y in { (4*130^(1/2)+8)/(-18), (8-4*130^(1/2))/(-18)}
(y-((4*130^(1/2)+8)/(-18)))*(y-((8-4*130^(1/2))/(-18))) = 0
((y-((4*130^(1/2)+8)/(-18)))*(y-((8-4*130^(1/2))/(-18))))/8 = 0
((y-((4*130^(1/2)+8)/(-18)))*(y-((8-4*130^(1/2))/(-18))))/8 = 0 // * 8
(y-((4*130^(1/2)+8)/(-18)))*(y-((8-4*130^(1/2))/(-18))) = 0
( y-((4*130^(1/2)+8)/(-18)) )
y-((4*130^(1/2)+8)/(-18)) = 0 // + (4*130^(1/2)+8)/(-18)
y = (4*130^(1/2)+8)/(-18)
( y-((8-4*130^(1/2))/(-18)) )
y-((8-4*130^(1/2))/(-18)) = 0 // + (8-4*130^(1/2))/(-18)
y = (8-4*130^(1/2))/(-18)
y in { (4*130^(1/2)+8)/(-18), (8-4*130^(1/2))/(-18) }
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