?。?)g(x)=lnx - 2(x-1)(x+1)
=-2x²+lnx+2
g′(x)=-4x+ 1/x
=(1+2x)(1-2x)
當x>1/2,g′(x)>0, 既當 x>1/2時,g(x)為增函數(shù)
當x=1時,g(x)=0,而g(x)又是在x>1/2時的增函數(shù)
∴在X>1時,g(x)>0恒成立;
?。?)g(x)=lnx - 2(x-1)(x+1)
=-2x²+lnx+2
g′(x)=-4x+ 1/x
=(1+2x)(1-2x)
當x>1/2,g′(x)>0, 既當 x>1/2時,g(x)為增函數(shù)
當x=1時,g(x)=0,而g(x)又是在x>1/2時的增函數(shù)
∴在X>1時,g(x)>0恒成立;