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D( t )
t^2+9*t+20 = 0
t+5 = 0
t+4 = 0
t^2+9*t+20 = 0
t^2+9*t+20 = 0
t^2+9*t+20 = 0
DELTA = 9^2-(1*4*20)
DELTA = 1
DELTA > 0
t = (1^(1/2)-9)/(1*2) or t = (-1^(1/2)-9)/(1*2)
t = -4 or t = -5
t+5 = 0
t+5 = 0
t+5 = 0 // - 5
t = -5
t+4 = 0
t+4 = 0
t+4 = 0 // - 4
t = -4
t in (-oo:-5) U (-5:-4) U (-4:+oo)
1/(t+4)+9/(t+5) = 1/(t^2+9*t+20) // - 1/(t^2+9*t+20)
1/(t+4)+9/(t+5)-(1/(t^2+9*t+20)) = 0
1/(t+4)+9/(t+5)-(t^2+9*t+20)^-1 = 0
1/(t+4)+9/(t+5)-1/(t^2+9*t+20) = 0
t^2+9*t+20 = 0
t^2+9*t+20 = 0
t^2+9*t+20 = 0
DELTA = 9^2-(1*4*20)
DELTA = 1
DELTA > 0
t = (1^(1/2)-9)/(1*2) or t = (-1^(1/2)-9)/(1*2)
t = -4 or t = -5
(t+5)*(t+4) = 0
1/(t+4)+9/(t+5)-1/((t+5)*(t+4)) = 0
(1*(t+5))/((t+4)*(t+5))+(9*(t+4))/((t+4)*(t+5))-1/((t+4)*(t+5)) = 0
1*(t+5)+9*(t+4)-1 = 0
10*t-1+41 = 0
10*t+40 = 0
(10*t+40)/((t+4)*(t+5)) = 0
(10*t+40)/((t+4)*(t+5)) = 0 // * (t+4)*(t+5)
10*t+40 = 0
10*t+40 = 0 // - 40
10*t = -40 // : 10
t = -40/10
t = -4
t in { -4}
t belongs to the empty set
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