Question 1023113
You did not write the equation that you have.  Your shown equation, 1/r=1/r^1+1/r^2, means  {{{1/r=1/r^1+1/r^2}}}, and has no such "R2".


Write the equation properly; most likely  1/r=1/r[1]+1/r[2] if pure text to be rendered in this online site; and would be   {{{1/r=1/r[1]+1/r[2]}}} when given the rendering tags.


Solving for {{{r[2]}}} will use your already-learned fraction or rational expressions skills.  The needed skills do not change once you begin using variables instead of plain constant real numbers.


{{{1/r-1/r[1]=1/r[2]}}}


{{{(1/r)(r[1]/r[1])-(1/r[1])(r/r)=1/r[2]}}}


{{{(r[1]-r)/(r*r[1])=1/r[2]}}}


Their reciprocals will also be equal...


{{{highlight(r[2]=(r*r[1])/(r[1]-r))}}}