Solve this formula for R.  Simplify your answer. 1/R = 1/a+1/b Use parenthesis around any polynomials in the numerator and/or denominator.

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violy's profile pic

violy | High School Teacher | (Level 1) Associate Educator

Posted on

Multiply both sides by the LCD which is abR to get rid of the denominators. 

`(abR)(1)/(R) = (abR)(1/a + 1/b) `

`(abR)/(R) = ((abR)/a + (abR)/b)`

Cancel out the common factor on top and bottom. 

`ab = bR + aR`

Factor out R on right side. 

`ab = R(b + a)`

Isolate the R on right side by dividing both sides by (b + a). 

`(ab)/(b + a) = (R(b+a))/(b+a)`

Therefore, R = (ab)/(b + a) or R = (ab)/(a + b).


paduncan's profile pic

paduncan | High School Teacher | (Level 1) Adjunct Educator

Posted on

1/R = 1/a +1/b

Common denominator is Rab

Multiply each term by common denominator Rab

ab = Rb + Ra

Use parentheses to simplify

ab = R(b+a)

Divide both sides of equation by (b+a) to solve for R

ab/(b+a) = R


pramodpandey's profile pic

pramodpandey | College Teacher | (Level 3) Valedictorian

Posted on


`` Taking lcm on RHS.


cross multiply


divide both side by (a+b)



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