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**1. Homework Statement**

The electric power in Watts produced is given by p= 144r/(r+.8)^2

where r is the resistance in ohms.

For what value of r is the power P a maximum?

**2. Homework Equations**

**3. The Attempt at a Solution**

Using the quotient rule i found a derivative of..

dp/dt= 144(-r+.8) / (r + .8)^3

Now I need to set this equal to zero and solve for R?

Multiplying the demonminator by 0 would leave me with just the numerator giving me..

-144r + 115.2 = 0

Solving for r gives me r = 0.8ohms

Was there maybe a problem with my derivative?