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Evaluate the following limit : limx→0[x⋅tanx1-cosx]

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Question

Evaluate the following limit :

`lim_(x -> 0) [(x*tanx)/(1 - cosx)]`

Sum
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Solution

`lim_(x -> 0) (xtanx)/(1 - cosx)`

= `lim_(x -> 0) (xtanx)/(1 - cos x) xx (1 + cosx)/(1 + cosx)`

= `lim_(x -> 0) (xtanx(1 + cosx))/(1 - cos^2x)`

= `lim_(x -> 0) (xtanx(1 + cosx))/(sin^2x)`

= `lim_(x -> 0) ((tanx/x)(1 + cos x))/((sin^2x/x^2))` ...[∵ x → 0, x ≠ 0]

= `([lim_(x -> 0) tanx/x] xx [lim_(x -> 0) (1 + cosx)])/[lim_(x -> 0) sinx/x]^2`

= `(1 xx [1 + cos 0])/1^2`

= 1 + 1

= 2.

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Chapter 7: Limits - Exercise 7.4 [Page 148]

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