# 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 $$\left. \frac{d^2P(R_L)}{dR^2_L} \right|_{R_L=R_{Th}} = -\frac{V^2_{Th}}{8R_{Th}} < 0$$