高数定积分求解
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(5)
(x²+x+1)/(x-1)=[x(x-1)+2(x-1)+3]/(x-1)
=x+2+3/(x-1)
lim(x→∞){[(x²+x+1)/(x-1)]sin(1/x)}
=lim(x→∞) xsin(1/x) + 2lim(x→∞) sin(1/x) +3lim(x→∞) sin(1/x)/(x-1)
=lim(x→∞) xsin(1/x)
=lim(x→∞) sin(1/x) /(1/x)
=lim(x→∞) cos(1/x)
=1
∫0→+∞ k/(x²+1)dx
=karctanx|0→+∞
=kπ/2=1
k=2/π
(7)两边同时对x求导得
e^y² dy/dx=-2xcosx²-2ysiny²dy/dx
(e^y²+2ysiny²)dy=-2xcosx²dx
dy=-2xcosx²dx/(e^y²+2ysiny²)
(x²+x+1)/(x-1)=[x(x-1)+2(x-1)+3]/(x-1)
=x+2+3/(x-1)
lim(x→∞){[(x²+x+1)/(x-1)]sin(1/x)}
=lim(x→∞) xsin(1/x) + 2lim(x→∞) sin(1/x) +3lim(x→∞) sin(1/x)/(x-1)
=lim(x→∞) xsin(1/x)
=lim(x→∞) sin(1/x) /(1/x)
=lim(x→∞) cos(1/x)
=1
∫0→+∞ k/(x²+1)dx
=karctanx|0→+∞
=kπ/2=1
k=2/π
(7)两边同时对x求导得
e^y² dy/dx=-2xcosx²-2ysiny²dy/dx
(e^y²+2ysiny²)dy=-2xcosx²dx
dy=-2xcosx²dx/(e^y²+2ysiny²)
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