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x in (-oo:+oo)
A = (1/2)*h*(a+b) // - (1/2)*h*(a+b)
A-((1/2)*h*(a+b)) = 0
(-1/2)*h*(a+b)+A = 0
A-1/2*h*(a+b) = 0
A-1/2*h*(a+b) = 0
A-1/2*a*h-1/2*b*h = 0
A-1/2*a*h-1/2*b*h = 0
x belongs to the empty set
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