19931992²/19931991²+19931993²-2=多少
问题描述:
19931992²/19931991²+19931993²-2=多少
答
u=x^2+1,则u'=2x
v=√u,则v=1/(2√u)*u'
y=lnv,则y'=1/v*v'
所以y'=1/v*1/(2√u)*2x
=2x/[√(x^2+1)*2√x^2+1)]
=x/(x^2+1)
答
令a=19931992
则原式=a²/[(a-1)²+(a+1)²-2]
=a²/(a²-2a+1+a²+2a+1-2)
=a²/(2a²)
=1/2