y=x/(x^2+3)求导
问题描述：
y=x/(x^2+3)求导
答
y=x/(x²+3)
y'=1/(x²+3)²·[(x²+3)-x(2x)]
=1/(x²+3)²·(x²+3-2x²)
=(3-x²)/(x²+3)²
用商法则:(u/v)'=(vu'-uv')/v²