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D( a )
a-7 = 0
a+8 = 0
a-7 = 0
a-7 = 0
a-7 = 0 // + 7
a = 7
a+8 = 0
a+8 = 0
a+8 = 0 // - 8
a = -8
a in (-oo:-8) U (-8:7) U (7:+oo)
(-2*a)/(a+8) = 2/(a-7) // - 2/(a-7)
(-2*a)/(a+8)-(2/(a-7)) = 0
(-2*a)/(a+8)-2*(a-7)^-1 = 0
(-2*a)/(a+8)-2/(a-7) = 0
(-2*a*(a-7))/((a+8)*(a-7))+(-2*(a+8))/((a+8)*(a-7)) = 0
-2*a*(a-7)-2*(a+8) = 0
12*a-2*a^2-16 = 0
12*a-2*a^2-16 = 0
2*(6*a-a^2-8) = 0
6*a-a^2-8 = 0
DELTA = 6^2-(-8*(-1)*4)
DELTA = 4
DELTA > 0
a = (4^(1/2)-6)/(-1*2) or a = (-4^(1/2)-6)/(-1*2)
a = 2 or a = 4
2*(a-2)*(a-4) = 0
(2*(a-2)*(a-4))/((a+8)*(a-7)) = 0
(2*(a-2)*(a-4))/((a+8)*(a-7)) = 0 // * (a+8)*(a-7)
2*(a-2)*(a-4) = 0
( a-2 )
a-2 = 0 // + 2
a = 2
( a-4 )
a-4 = 0 // + 4
a = 4
a in { 2, 4 }
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