If it's not what You are looking for type in the equation solver your own equation and let us solve it.
x in (-oo:+oo)
r = (1/2)*(a+b) // - (1/2)*(a+b)
r-((1/2)*(a+b)) = 0
(-1/2)*(a+b)+r = 0
r-1/2*(a+b) = 0
r-1/2*(a+b) = 0
r-1/2*a-1/2*b = 0
r-1/2*a-1/2*b = 0
x belongs to the empty set
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