Question 371983
multiplying by r1+r2 ___ r1Rt + r2Rt = r1r2


subtracting r2Rt ___ r1Rt = r1r2 - r2Rt


factoring ___ r1Rt = r2(r1 - Rt)


dividing by r1-Rt ___ (r1Rt) / (r1 - Rt) = r2