Question 663050
{{{1/R=1/A+1/B}}}


{{{1/R-1/A=1/B}}}......on the left side find LCD


{{{(1*A-1*R)/RA=1/B}}}


{{{(A-R)/RA=1/B}}}...........cross multiply


{{{(A-R)B=1*RA}}}


{{{B=RA/(A-R)}}}