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Let ,when,and iff(x)={kcosxπ-2x,when x≠π23,x=π2 and if f(x)=f(π2) find the value of k.

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प्रश्न

Let `f(x) = {{:((k cos x)/(pi - 2x)",", "when"  x ≠ pi/2),(3",", x = pi/2  "and if"  f(x) = f(pi/2)):}` find the value of k.

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उत्तर

Given, `f(x) = {{:((k cos x)/(pi - 2x)",",  x ≠ pi/2),(3",",  x = pi/2):}`

L.H.L, `f(x) = lim_(x -> pi^-/2) (k cos x)/(pi - 2x)`

= `lim_(h -> 0) (k cos (pi/2 - h))/(pi - 2(pi/2 - h))`

= `lim_(h -> 0) (k sin h)/(pi - pi + 2h)`

= `lim_(h -> 0) (k sin h)/(2h)`

= `l/2 * 1`

= `k/2`  ......`[because  lim_(h -> 0) sinh/h = 1]`

R.H.L. `f(x) = lim_(x -> pi^+/2) (k cos x)/(pi - 2x)`

= `lim_(h -> 0) (k cos (pi/2 + h))/(pi - 2(pi/2 + h))`

= `lim_(h -> 0) (-k sin h)/(pi - pi - 2h)`

= `lim_(h -> 0) (-k sin h)/(-2h)`

= `k/2`  ....`[because  lim_(h -> 0)  sinh/h = 1]`

We are given that `lim_(x -> pi/2) f(x)` = 3

So, `k/2` = 3

⇒ k = 6

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अध्याय 13: Limits and Derivatives - Exercise [पृष्ठ २४२]

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एनसीईआरटी एक्झांप्लर Mathematics [English] Class 11
अध्याय 13 Limits and Derivatives
Exercise | Q 52 | पृष्ठ २४२

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