= lim & ltx→0 & gt； ln( 1+x？ )/[( 1/cosx)-cosx]
= lim & ltx→0 & gt； cosx ln( 1+x？ )/( 1-cos？ x)
= lim & ltx→0 & gt； ln( 1+x？ )/sin? x
= lim & ltx→0 & gt； 【2x/( 1+x？ )]/(2sinxcosx)
= lim & ltx→0 & gt； 【2x/( 1+x？ )]/(sin2x)
= lim & ltx→0 & gt； 2x/(sin2x)
= 1
(1) How does the natural gas ladder charge work?
Cities are different, one more step is expensive, and two more steps are expensive.