已知x,y,z大于零,3的x次方=4的y次方=6的z次方,求1/z-1/x=1/2y;比较3x;4y;6z的大小
问题描述：
已知x,y,z大于零,3的x次方=4的y次方=6的z次方,求1/z-1/x=1/2y;比较3x;4y;6z的大小
答
设3^x=4^y=6^z=k.(k>1)
x=log3(k)
y=log4(k)
z=log6(k)
1/z-1/x=logk(6)-logk(3)=logk(2)
1/(2y)=1/2*logk(4)=logk(2)
故:1/z-1/x=1/(2y)
1/(3x)=1/3*logk(3)=logk(3^1/3)
1/(4y)=1/4*logk(4)=logk(4^1/4)
1/(6z)=1/6*logk(6)=logk(6^1/6)
由于logk(3^1/3)>logk(4^1/4)>logk(6^1/6)
所以,1/3x>1/4y>1/6z
即3x