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महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता ११ वी

Evaluate the following: limx→π2[cos3x+3cosx(2x-π)3] - Mathematics and Statistics

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प्रश्न

Evaluate the following:

`lim_(x -> pi/2) [(cos3x + 3cosx)/(2x - pi)^3]`

मूल्यांकन

उत्तर

Put x = `pi/2 + "h"`.

Then as `x -> pi/2, "h" -> 0`.

Also, 2x – π = `2(pi/2 + "h") - pi` = π + 2h  – π = 2h

∴ `lim_(x -> pi/2) [(cos3x + 3cosx)/(2x - pi)^3]`

 = `lim_(x -> pi/2) (4cos^3x - 3cosx + 3cosx)/(2x - pi)^3`

= `lim_(x -> pi/2) (4cos^3x)/(2x - pi)^3`

= `lim_("h" -> 0) (4[cos (pi/2 + "h")]^3)/(2"h")^3`

= `lim_("h" -> 0) (4( - sin "h")^3)/(8"h"^3)`

= `-4/8 lim_("h" -> 0) (sin"h"/"h")^3`

= `-1/2 (lim_("h" -> 0) sin"h"/"h")^3`

= `-1/2(1)^3`

= `-1/2`

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Substitution Method
  या प्रश्नात किंवा उत्तरात काही त्रुटी आहे का?
पाठ 7: Limits - Exercise 7.5 [पृष्ठ १५१]

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