答:
y=4/(e^x+1)
求导:y'(x)=-4(e^x)/(e^x+1)^2=tana
取倒数得:-4/tana=[(e^x+1)^2]/e^x
=(e^2x+2e^x+1)/e^x
=e^x+2+1/e^x
>=2√[(e^x)*1/e^x]+2
=2+2
=4
所以:1/tana
答:
y=4/(e^x+1)
求导:y'(x)=-4(e^x)/(e^x+1)^2=tana
取倒数得:-4/tana=[(e^x+1)^2]/e^x
=(e^2x+2e^x+1)/e^x
=e^x+2+1/e^x
>=2√[(e^x)*1/e^x]+2
=2+2
=4
所以:1/tana