3.求下列极限:-|||-(1) lim _(xarrow 0)dfrac (2{x)^2+3x+1}(sin x+2) ;-|||-(3) lim _(xarrow infty )dfrac ({({x)^2-3)}^20}(4{x)^40+8(x)^20+1} =-|||-(5) lim _(narrow infty )n(sqrt ({n)^2+1}-sqrt ({n)^2-1}) ;-|||-(7) lim _(xarrow 0)dfrac ({(1+x))^n-1}(x) ;-|||-(2) lim _(xarrow 1)dfrac ({x)^2-2x+1}(1-{x)^3}-|||-(4) lim _(narrow infty )dfrac ({(3{n)^2+2)}^20(2(n)^8-1)}({(5{n)^16+3n+1)}^2((n+2))^16} ;-|||-(6) lim _(xarrow 2)dfrac (x+3)({x)^2-4x+4} =-|||-(8) lim _(narrow infty )(1-dfrac (1)({2)^2})(1-dfrac (1)({3)^2})... (1-dfrac (1)({n)^2}) -