u=x²+1
则u'=2x
v=√u
则v'=1/(2√u)*u'
y=1/v
所以y'=-1/v²*v'
=-1/(x²+1)*1/[2√(x²+1)]*u'
=-1/(x²+1)*1/[2√(x²+1)]*2x
=-x/[(x²+1)√(x²+1)]
u=x²+1
则u'=2x
v=√u
则v'=1/(2√u)*u'
y=1/v
所以y'=-1/v²*v'
=-1/(x²+1)*1/[2√(x²+1)]*u'
=-1/(x²+1)*1/[2√(x²+1)]*2x
=-x/[(x²+1)√(x²+1)]