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This is the expression: [(a-1)/(3a+(a-1)^2) - (1-3a+a^2)/(a^3-1) -1/(a-1)] / (a^2+1)/(1-a), result should be 1/(a^2+a+1). I don't know where to start :S. I've reached now the more advanced exercises, which I can see cause I have no idea what to do with this one. Could someone walk me through...