韶关细细粒
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三、1.左极限=lim(x->0-)f(x)=lim(x->0-)(-x/x)=-1
右极限=lim(x->0+)f(x)=lim(x->0+)(x/x)=1
∵左极限≠右极限
∴f(x)在x=0点处不存在极限;
2.左极限=lim(x->2-)f(x)=lim(x->2-)(x+2)=4
右极限=lim(x->2+)f(x)=lim(x->2+)[1/(x-2)]=+∞
∵左极限≠右极限
∴f(x)在x=2点处不存在极限;
四、∵lim(x->∞)[(x^2+1)/(x+1)-x-b]=1/2
==>lim(x->∞)[((1-a)x^2-(a+b)x+(1-b))/(x+1)]=1/2
==>lim(x->∞)[((1-a)x-(a+b)+(1-b)/x)/(1+1/x)]=1/2 (分子分母同除x)
==>1-a=0,-(a+b)=1/2
∴a=1,b=-3/2.
1年前
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韶关细细粒
1.原式=[lim(x->0)(x^2)]*[lim(x->0)(sin(1/x))]
=0*[lim(x->0)(sin(1/x))]
=0 (-1≤[lim(x->0)(sin(1/x))]≤1是有限值);
2.原式=[lim(x->∞)(1/x)]*[lim(x->∞)(arctanx)]
=0*(±π/2)
=0;
3.原式=[lim(x->∞)(1/√x)]*[lim(x->∞)(sinx)]
=0*[lim(x->∞)(sinx)]
=0 (-1≤[lim(x->∞)(sinx)]≤1是有限值)。