令a=ln(x^2)
则先对a^3求导,再对ln求导,最后对x^2求导
所以[ln^3(x^2)+3]'
=[ln^3(x^2)]'
=3[ln(x^2)]^2*[ln(x^2)]'
=3[ln(x^2)]^2*(1/x^2)*(x^2)'
=6x[ln(x^2)]^2*(1/x^2)
=(6/x)*[ln(x^2)]^2