Resistor in Parallel

${\displaystyle {\frac {1}{R_{t}}}={\frac {1}{R_{1}}}+{\frac {1}{R_{2}}}+....+{\frac {1}{R_{n}}}}$

Voltage Divivider

${\displaystyle {\frac {v_{o}}{v_{i}}}={\frac {R_{2}}{R_{2}+R_{1}}}}$

Current Divider

Pie Network

${\displaystyle {\frac {v_{o}}{v_{i}}}={\frac {R_{3}+R_{2}}{R_{1}+R_{2}}}}$

Tee Network

${\displaystyle {\frac {v_{o}}{v_{i}}}={\frac {R_{3}}{R_{1}}}({\frac {R_{3}-R_{2}}{R_{1}-R_{2}}})}$

Wien Bridge Network