已知x+1/x=3,求x^2/(x^4+x^2+1)的值!我不太会做,请大家帮帮忙,要有过程谢谢!!还有一道:先化简后求值![4/(x^2-y^2)+(x+y)/(x*y^2-x^2*y)]/[(x^2+xy-2*y^2)/x^2*y+2x*y^2)]其中x=2,y=-3,请写上过程,谢谢!!!!!!!!!!非常感谢!!!!!!!!!