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x in (-oo:+oo)
h*((a+b)/2) = a // - a
h*((a+b)/2)-a = 0
(h*(a+b))/2-a = 0
(h*(a+b))/2+(2*(-a))/2 = 0
h*(a+b)+2*(-a) = 0
a*h-2*a+b*h = 0
(a*h-2*a+b*h)/2 = 0
(a*h-2*a+b*h)/2 = 0 // * 2
a*h-2*a+b*h = 0
x belongs to the empty set
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