lim sinx-cosx / 1-tanx
x->pi/4
=lim(sinx-cosx)'/lim(1-tanx)'(洛必达法则)
=lim(cosx+sinx)/lim(-(secx)^2)
==lim-(cosx)^2(cosx+sinx)
=-1/2*√2
=-√2/2
lim sinx-cosx / 1-tanx
x->pi/4
=lim(sinx-cosx)'/lim(1-tanx)'(洛必达法则)
=lim(cosx+sinx)/lim(-(secx)^2)
==lim-(cosx)^2(cosx+sinx)
=-1/2*√2
=-√2/2