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D( y )
y = 0
y = 0
y = 0
y in (-oo:0) U (0:+oo)
9/y+8/7 = (7/7)*y // - (7/7)*y
9/y-((7/7)*y)+8/7 = 0
9/y-y+8/7 = 0
9*y^-1-1*y^1+8/7*y^0 = 0
(8/7*y^1-1*y^2+9*y^0)/(y^1) = 0 // * y^2
y^1*(8/7*y^1-1*y^2+9*y^0) = 0
y^1
(8/7)*y-y^2+9 = 0
(8/7)*y-y^2+9 = 0
DELTA = (8/7)^2-(-1*4*9)
DELTA = 1828/49
DELTA > 0
y = ((1828/49)^(1/2)-(8/7))/(-1*2) or y = (-(8/7)-(1828/49)^(1/2))/(-1*2)
y = ((1828/49)^(1/2)-8/7)/(-2) or y = ((1828/49)^(1/2)+8/7)/2
y in { ((1828/49)^(1/2)-8/7)/(-2), ((1828/49)^(1/2)+8/7)/2}
y in { ((1828/49)^(1/2)-8/7)/(-2), ((1828/49)^(1/2)+8/7)/2 }
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