1.用洛必达法则求下列极限.-|||-(1) lim _(xarrow 0)dfrac (ln (1+x))(x) :-|||-(3) lim _(xarrow a)dfrac (sin x-sin a)(x-a)-|||-(5) lim _(xarrow dfrac {pi )(2)}dfrac (ln sin x)({(pi -2x))^2} ,-|||-(7) lim _(xarrow {0)^+}dfrac (ln tan 7x)(ln tan 2x) .-|||-(9) lim _(xarrow +infty )dfrac (ln (1+dfrac {1)(x))}(arctan x) ,-|||-(11)limxcot2x;-|||-(13) lim _(xarrow 1)(dfrac (2)({x)^2-1}-dfrac (1)(x-1)) ;-|||-(15) limx^sinx;-|||-(17) lim _(xarrow {0)^+}((ln dfrac {1)(x))}^x :-|||-(2) lim _(xarrow 0)dfrac ({e)^x-(e)^-x}(sin x)-|||-(4) lim _(xarrow pi )dfrac (sin 3x)(tan 5x) .-|||-(6) lim _(xarrow a)dfrac ({x)^m-(a)^m}({x)^n-(a)^n} ;-|||-(8) lim _(xarrow dfrac {pi )(2)}dfrac (tan x)(tan 3x) .-|||-(10) lim _(xarrow 0)dfrac (x-sin x)(sin {x)^3} ;-|||-(12) lim _(xarrow 0)(x)^2(e)^dfrac (1{{x)^2}} ;-|||-(14) lim _(xarrow infty )((1+dfrac {a)(x))}^x :-|||-(16) lim _(xarrow 0)((1+sin x))^dfrac (1{x)} ;-|||-(18) lim _(xarrow +infty )((x+sqrt {1+{x)^2})}^dfrac (1{x)} -