Solve each formula for the specified variable

Question

I=E/(RL+r) for r

Answer 1

The equation is I = E/(RL + r) and solve for r.

Multiply each side by (RL + r).

I * (RL + r) = [E/(RL + r)] * (RL + r)

I * (RL + r) = E

Divide each side by I.

[I * (RL + r)]/I = E/I

RL + r = E/I

Subtract RL from each side.

RL + r - RL = (E/I) - RL

r = (E/I) - RL

The value of r = (E/I) - RL.