高数 极限 limx→1 [lnx-sin(x-1)]/[三次根号下(2x-x²)-1]

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高数 极限 limx→1 [lnx-sin(x-1)]/[三次根号下(2x-x²)-1]

高数 极限 limx→1 [lnx-sin(x-1)]/[三次根号下(2x-x²)-1]
高数 极限 limx→1 [lnx-sin(x-1)]/[三次根号下(2x-x²)-1]

高数 极限 limx→1 [lnx-sin(x-1)]/[三次根号下(2x-x²)-1]
你要知道一个等价无穷小
x->0,(1+x)^a~ax
而(2x-x^2)^(1/3)=[1-(x-1)^2]^(1/3)~(-1/3)(x-1)^2
设x-1=t
原式变为lim t->0, [ln(1+t)-sint]/[(-1/3)t^2]
=lim t->0 [t-t^2/2+o(t^2)-t+o(t^2)]/[(-1/3)t^2]
=lim t->0,[(-1/2)t^2+o(t^2)]/[(-1/3)t^2]
=3/2

limx→1 [lnx-sin(x-1)]/[三次根号下(2x-x²)-1]
= limx→1 [1/x-cos(x-1)]/[(2x-x²)^(-2/3)*(2-2x)]
=1/2*limx→1[1-xcos(x-1)]/(1-x)
=1/2*limx→1[-cos(x-1)+xsin(x-1)]/(-1)
=1/2
(连续...

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limx→1 [lnx-sin(x-1)]/[三次根号下(2x-x²)-1]
= limx→1 [1/x-cos(x-1)]/[(2x-x²)^(-2/3)*(2-2x)]
=1/2*limx→1[1-xcos(x-1)]/(1-x)
=1/2*limx→1[-cos(x-1)+xsin(x-1)]/(-1)
=1/2
(连续运用罗比塔法则)

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