第1个回答 2019-07-21
解析:∵x^(1/2)+x^(-1/2)=3
∴x+2+1/x=9,
x+1/x=7
∴x^2+2+x^(-2)=49
∴x^2+x^(-2)=47
[x^(3/2)+x^(-3/2)]/[x^2-2+x^(-2)]
=[x^(1/2)+x^(-1/2)](x-1+1/x)/[x^2-2+x^(-2)]
=3*(7-1)/(47-2)
=18/45
=2/5
2题:假设正方形DEFG的顶点D,E点落在AB上,F在BC上,G在AC上,设边长=x,
过C做CM⊥AB于M,交FG于N,
∵角c=90度
AC=3
BC=4
∴AB=5
S=3*4/2=AB*CM/2=5CM/2
得CM=12/5
∵FG‖AB,∴△CFG∽△CBA
∴FG/AB=CN/CM
x/5=(12/5-x)/(12/5)
解得x=60/37