\(\frac{E}{e}=\frac{R+r}{R-r}\)
Multiply both sides of the equation by (R - r) .
\((R-r)\,*\,\frac{E}{e}=R+r\)
Distribute the \( \frac{E}{e} \) .
\(R*\frac{E}{e}\,-\,r*\frac{E}{e}=R+r\)
Add \( r*\frac{E}{e} \) to both sides of the equation.
\(R*\frac{E}{e}=R+r+r*\frac{E}{e}\)
Subtract R from both sides of the equation.
\(R*\frac{E}{e}-R=r+r*\frac{E}{e}\)
Factor out an r on the right side.
\(R*\frac{E}{e}-R=r(1+\frac{E}{e})\)
Divide both sides of the equation by \( (1+\frac{E}{e}) \) .
\(\frac{R*\frac{E}{e}-R}{1+\frac{E}{e}}=r\)
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