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Question Number 69607 by malwaan last updated on 25/Sep/19

without using lhospital please  prove that  lim_(x→0)  ((x−sin x)/x^3 ) = (1/6)  I want every method  possible because someone  challenge me

withoutusinglhospitalpleaseprovethatlimx0xsinxx3=16Iwanteverymethodpossiblebecausesomeonechallengeme

Commented by mathmax by abdo last updated on 26/Sep/19

we have  sinx =Σ_(n=0) ^∞  (((−1)^n x^(2n+1) )/((2n+1)!)) =x−(x^3 /(3!)) +(x^5 /(5!)) −(x^7 /(7!)) +... ⇒  −sinx =−x+(x^3 /(3!))−(x^5 /(5!)) +(x^7 /(7!)) +o(x^7 ) ⇒x−sinx =  (x^3 /(3!))−(x^5 /(5!)) +(x^7 /(7!)) +o(x^7 ) ⇒((x−sinx)/x^3 ) =(1/(3!))−(x^2 /(5!)) +(x^4 /(7!)) +o(x^4 ) ⇒  lim_(x→0)    ((x−sinx)/x^3 ) =(1/(3!)) =(1/6)

wehavesinx=n=0(1)nx2n+1(2n+1)!=xx33!+x55!x77!+...sinx=x+x33!x55!+x77!+o(x7)xsinx=x33!x55!+x77!+o(x7)xsinxx3=13!x25!+x47!+o(x4)limx0xsinxx3=13!=16

Commented by Prithwish sen last updated on 25/Sep/19

lim_(x→0)  ((x−(x−(x^3 /(3!))+(x^5 /(5!))−....))/x^3 ) = lim_(x→0)   (1/(3!)) − (x^2 /(5!)) + the higher power of x  = (1/(3!)) = (1/6)  proved

limx0x(xx33!+x55!....)x3=limx013!x25!+thehigherpowerofx=13!=16proved

Commented by malwaan last updated on 26/Sep/19

thank you sir

thankyousir

Commented by malwaan last updated on 27/Sep/19

thank you so much

thankyousomuch

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