Deutsche Version 

V comes from "voltage" and E from "electromotive force emf". E means also energy, so let's choose V. Energy = voltage × charge. E = V × Q. Some like better to stick to E instead to V, so do it. 
Voltage V = I × R = P / I = √(P × R) in volts V Current I = V / R = P / V = √(P / R) in amperes A Resistance R = V / I = P / I^{2 } = V^{2}/ P in ohms Ω Power P = V × I = R × I^{2}= V^{2}/ R in watts W 
In sound engineering there is no Power matching or Impedance matching. In audio we use only Voltage bridging or high Impedance bridging Z_{out} < Z_{in.} This includes also the connection from the power amplifier to the speaker. 
If the unit of power P = I × V and of voltage V = I · R is needed
look for "The Big Power Formulas":
Calculations: Power (watt), voltage, current, and resistance
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