# Explain this line of working when solving for the maximum power of a load resistor

Please, can you explain this line of working from the maximum power transfer theorem:

For maximum power dissipation in the load, the condition given below must be satisfied $$\left. \frac{d^2P(R_L)}{dR^2_L} \right|_{R_L=R_{Th}} = -\frac{V^2_{Th}}{8R_{Th}} < 0$$

It's from this page: Maximum Power Transfer Theorem Assignment Help.

• Your first link seems to go to an image sharing site with an unhelpful image. Your second link goes to a page that explains the maximum power transfer theorem. What part of their explanation are you having trouble with? – The Photon Aug 20 '14 at 22:18
• @ThePhoton you have to click on the unhelpful image and it expands and highlights the second derivative test, which I think is what the OP is confused about. – John D Aug 20 '14 at 23:01