x^2/3,-x^3/15,x^4/35,-x^5/63,x^6/99,照此规律,第十个式子是( ),第n个识式子是(

问题描述:

x^2/3,-x^3/15,x^4/35,-x^5/63,x^6/99,照此规律,第十个式子是( ),第n个识式子是(

[(-X)^(n+1)]/(4n^2-1)
分子就不证了
分母为
3=1x3
15=3x5
35=5x7
63=7x9
...
(2n-1)x(2n+1)