高数极限定义(高数极限)
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1、5) 求极限部分:1/(1-x) - 3/(1-x^3) =[ (1+x+x^2)-3]/(1-x^3) = (x^2+x-2)/(1-x^3)=(x+2)(x-1) /(1-x^3)
2、= -(x+2)/(x^2+x+1)。当x-->0时,极限=-(1+2)/(1+1+1)=-1
3、13) (5-x^2)^(1/2) +x-3= [(5-x^2)^(1/2) +(x-3)]* [(5-x^2)^(1/2) -(x-3)]/[(5-x^2)^(1/2) -(x-3)]
4、 = -2(x-1)(x-2) /[(5-x^2)^(1/2) -(x-3)]
5、 (x-1)^(1/2)-1= [(x-1)^(1/2)-1] *[(x-1)^(1/2)+1]/[(x-1)^(1/2)+1]=(x-2)/[(x-1)^(1/2)+1]
6、因此原求极限部分={-2(x-2) /[(5-x^2)^(1/2) -(x-3)]} /{(x-2)/{[(x-1)^(1/2)+1]}
7、=-2(x-1)[(x-1)^(1/2)+1]/[(5-x^2)^(1/2) -(x-3)]
8、当x-->2时,原极限=2(2-1)[(2-1)^(1/2)+1]/[(5-2^2)^(1/2) -(2-3)]
9、=2*2/ (1-2+3) = 2
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