这极限题怎么做,详细步骤
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lim(x→1)(tanπx/4)^(tanπx/2)
=lim(x→1)[1+(tanπx/4 -1)]^(tanπx/2)
=lim(x→1){[1+(tanπx/4-1)]^[1/(tanπx/4 -1)]}^[tanπx/2(tanπx/4 -1)].
∵lim(x→1)tanπx/2 (tanπx/4 -1)
=lim(x→1)(tanπx/4 -1)/ cotπx/2
=lim(x→1)π/4 sec^2 (πx/4)/[-π/2 csc^2 (πx/2)]
=-1/2 lim(x→1)sin^2 (πx/2)/cos^2 (πx/4)
=-1/2 * 1/(√2/2)^2=-1.
∴原极限=e^(-1)=1/e.
=lim(x→1)[1+(tanπx/4 -1)]^(tanπx/2)
=lim(x→1){[1+(tanπx/4-1)]^[1/(tanπx/4 -1)]}^[tanπx/2(tanπx/4 -1)].
∵lim(x→1)tanπx/2 (tanπx/4 -1)
=lim(x→1)(tanπx/4 -1)/ cotπx/2
=lim(x→1)π/4 sec^2 (πx/4)/[-π/2 csc^2 (πx/2)]
=-1/2 lim(x→1)sin^2 (πx/2)/cos^2 (πx/4)
=-1/2 * 1/(√2/2)^2=-1.
∴原极限=e^(-1)=1/e.
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