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Lim(tAnx%sinx)/x∧3

无穷近似值代换,二倍角公式 =lim(1-cosx)/x²limtanx/x =lim2sin²(x/2)/x² =lim2(x/2)²/x² =1/2

猜x→0时 (tanx-sinx)/x^3 →(sec^x-cosx)/(3x^2) →[(-2)(-sinx)/(cosx)^3+sinx]/(6x) →1/2.

lim(x→0) (tanx-sinx)/x∧3 =lim(x→0) (sinx/cosx-sinx)/x∧3 =lim(x→0) (1/cosx-1)/x∧2 * (sinx/x) =lim(x→0) (1-cosx)/x∧2 /cosx =lim(x→0) (1-cosx)/x∧2 =lim(x→0) 2 (sin (x/2) )^2/x∧2 =lim(x→0) 2(x/2)^2/x∧2 =1/2

lim(tanx-sinx/sin³x)=lim(1-cosx)/sin²x=lim 2sin²(x/2)/sin²x=(x²/2)/x²=1/2 x→0

因为tanx精确的说是近似与x/√(x*x+1),这类应用无穷近似值求极限不能简单粗暴的把lim(A+B)拆成=limA+limB,而得先应用三角函数转化,把(tanx-sinx)=(1-cosx)sinx/cosx=2sin(x/2)sin(x/2)sinx/cosx再应用替换,基本都必须把和差形变...

lim(x→0)(tanx-sinx)/(sinx)^3 =lim(x→0)tanx(1-cosx)/x^3 =lim(x→0)x*(1/2x^2)/x^3 =1/2

lim [(1+tanx)/(1+sinx)]^(1/x^3) =lim [1+(tanx-sinx)/(1+sinx)]^[(1+sinx)/(tanx-sinx)*(tanx-sinx)/(1+sinx)*1/x^3] =e^lim (tanx-sinx)/x^3 * 1/(1+sinx) =e^lim tanx(1-cosx)/x^3*1/(1+0) =e^lim (x*x^2/2)/x^3 =e^(1/2) =√e

(e^tanx-e^sinx)/x³ =(e^tanx-e^sinx)/(tanx-sinx)*(tanx-sinx)/x³ 而(e^tanx-e^sinx)/(tanx-sinx)=e^ξ,ξ在sinx与tanx之间 所以原式=e^ξ*(tanx-sinx)/x³ 当x→0时,ξ→0,利用等价替换tanx-sinx~x³/2可知原式=e^0*1/2=1/2

0/0型的极限不能随便拆项,因为这样可能造成上下无穷小的阶发生变化。 lim〔x→0〕(tanx-sinx)/x² =lim〔x→0〕(1-cosx)sinx/x²cosx =lim〔x→0〕(sin²x)sinx/x²cosx(1+cosx) =0/2 =0

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