Really need help!

Question

In an electrical circuit, when two resistors are connected in parallel, the effective resistance, R ohms (Ω), of the two resistors is given by the formula 1/R=1/R1+1/R2 where R1 and R2 are the resistances of the individual resistors in ohms. 

 

a) Make R the subject of the formula 1/R-1/R1+1/R2

 

b) hence, find the effective resistance of the two resistors if R1=2 and R2=3. 

 

Please help by showing the full working. I don't understand this question. 

Answer 1

a)

 

Simply solve for R from the equation         1 / R = (1 / R₁) + (1 / R₂)

 

 

Get the lowest common denominator (LCD) on the right side of equation.  LCD is R₁R₂.

 

1 / R = (R₂ + R₁) / R₁R₂

 

 

Cross-multiply.

 

R₁R₂ = R(R₁ + R₂)

 

 

R = R₁R₂ / (R₁ + R₂)

 

 

b)

 

Plug in the known values of the two resistors into the bolded formula from the last part.