Solve each formula for the specified variable

Question

I=E/R1+r for r

Answer 1

Given equation : I=E/(R₁+r)

Multiply each side by (R₁+r).

I(R₁+r)=E

Divide each side by I.

(R₁+r)=E/I

Subtract R₁ from each side.

r=(E/I)-R₁

The solution is r=(E/I)-R₁