lim(x→1) lncos(x-1)/(1-sin(πx/2))详细过程

lim(x→1) lncos(x-1)/(1-sin(πx/2))
令x-1=t,t→0
原式=lim(t→0) lncost/(1-sin(π(t+1)/2))
=lim(t→0) lncost/(1-cos(πt/2))
=lim(t→0) -sint/cost/(π/2*sin(πt/2))
=-2/πlim(t→0) sint/sin(πt/2)
=-2/π*2/π
=4/π^2

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