公式求导Pl=(Us/(Rs+Rl))^2*Rl求

公式求导Pl=(Us/(Rs+Rl))^2*Rl求 DPl/DRl,

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lnPI=2RI*ln[US/(Rs+RI)]=2RI(lnUS-ln(RS+RI)]
对上式求导后
(1/pi)dpi/dri=2ln[US/(Rs+RI)]-2RI/(Rs+RI)
dpi/dri={2ln[US/(Rs+RI)]-2RI/(Rs+RI)}(Us/(Rs+Rl))^2*Rl