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CLASS_11_MATHS_SOLUTIONS_NCERT

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

______________________________________________________________________________<br />

d<br />

d<br />

f '( x) x 3 -4x 3 4x<br />

x<br />

-4 -5 5 -4<br />

<br />

dx<br />

dx<br />

<br />

x<br />

<br />

x 04 5 x 34x 4<br />

-4 -5-1 -5 4 1<br />

x 20x 34x 4x<br />

-4 -6 -5 -5<br />

20x 12x 16x<br />

-10 -5 -10<br />

-10 -5<br />

36x<br />

12x<br />

12 36<br />

<br />

-5 10<br />

x x<br />

2<br />

2 x<br />

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

x1 3x1<br />

f’(x) = d 2<br />

2 d x <br />

<br />

dx x 1<br />

<br />

dx 3x<br />

1<br />

By quotient rule,<br />

d d d 2 2 d<br />

x 1 2 2 x 1<br />

<br />

3x 1 x x 3x<br />

1<br />

<br />

<br />

' <br />

dx dx <br />

dx dx <br />

f x 2 2 <br />

x1<br />

3x1<br />

<br />

<br />

2<br />

x<br />

10 21<br />

3x 12x x<br />

3<br />

<br />

2<br />

<br />

2<br />

x1<br />

3x1<br />

<br />

2 2<br />

2 6x 2x 3x<br />

<br />

<br />

2<br />

<br />

2<br />

<br />

x1 <br />

3x1<br />

<br />

2 2<br />

2 3x<br />

2x<br />

<br />

<br />

2<br />

<br />

2<br />

<br />

x1 3x1<br />

<br />

2<br />

x3x<br />

2<br />

<br />

2 2<br />

x1 3x1<br />

<br />

<br />

<br />

<br />

Question 10:<br />

Find the derivative of cos x from first principle.<br />

Solution 10:<br />

Let f (x) = cos x. Accordingly, from the first principle,<br />

f xh<br />

f x<br />

f ' x<br />

lim<br />

h 0<br />

h<br />

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