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CLASS_11_MATHS_SOLUTIONS_NCERT

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Class XI Chapter 13 – Limits and Derivatives Maths<br />

______________________________________________________________________________<br />

1 sin( x h)cos x sin xcos<br />

x h <br />

lim <br />

h0<br />

h cos x hcos<br />

x <br />

1 1 sin( x h x)<br />

<br />

lim <br />

cos x h0<br />

h cos x h<br />

<br />

1 1 sinh <br />

lim <br />

cos x h0<br />

h cos<br />

x h<br />

1 sinh 1 <br />

. lim . lim<br />

cos x<br />

<br />

h0 h<br />

h0<br />

cos x h<br />

<br />

<br />

1 1<br />

.1.<br />

cos x cos x0<br />

1<br />

<br />

2<br />

cos x<br />

2<br />

sec x<br />

<br />

<br />

ii<br />

<br />

x x <br />

2<br />

x x x x<br />

Therefore, from (i) and ii ,We obtain<br />

f' x cos (1 sec ) tan 1 sin<br />

2<br />

x cos x tan x x tan x1 sin x<br />

<br />

<br />

2<br />

tan x x cos x x tan x 1sin<br />

x<br />

<br />

<br />

Question 26:<br />

Find the derivative of the following functions (it is to be understood that a, b, c, d, p, q, r and s<br />

are fixed non<br />

zero constants and m and n are integers):<br />

Solution 26:<br />

Let f(x) = 4 x<br />

5sin x<br />

3x7cos<br />

x<br />

By quotient rule,<br />

f '<br />

x<br />

<br />

d<br />

dx<br />

4x5sin<br />

x<br />

3x7cos<br />

x<br />

3x 7cos x 4x 5sin x4x 5sin x 3x 7cos<br />

x<br />

3x7cos<br />

x 2<br />

d<br />

dx<br />

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