a1=P*((Y)*(R1+R2)/(Y+R1+R2))/(X+(Y)*(R1+R2)/(Y+R1+R2))*(R2/(R2+R1)), a2=(R2/(R2+R1))*P*Y*(R1+R2)/(Y+R1+R2)/(X*R3/(X+R3)+Y*(R1+R2)/(Y+R1+R2))

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