y=1/2(2的x次方+2的-x次方）判断它在0到正无穷上的单调性,并证明,急.

令x1>x2>0f(x1)-f(x2)=1/2[2^x1+1/2^x1-2^x2-1/2^x2]通分=1/2[2^2x1*2^x2-2^x1*2^2x2+2^x2-2^x1]/2^x1*2^x2分母大于0分子=2^x1*2^x2*(2^x1-2^x2)-(2^x1-2^x2)=(2^x1-2^x2)(2^x1*2^x2-1)x1>x2所以2^x1-2^x2>0x1>0,2^x...