NCERT Solutions
Class 11 - Mathematics - Chapter 12: LIMITS AND DERIVATIVES
EXERCISE 12.2

Question. 1

Find the derivative of \(x^{2}-2\) at \(x=10\).

Answer:

20

Question. 2

Find the derivative of \(x\) at \(x=1\).

Answer:

1

Question. 3

Find the derivative of \(99x\) at \(x=100\).

Answer:

99

Question. 4

Find the derivative of the following functions from first principle:

(i) \(x^{3} - 27\)

(ii) \((x-1)(x-2)\)

(iii) \(\dfrac{1}{x^{2}}\)

(iv) \(\dfrac{x+1}{x-1}\)

Answer:

(i) \(3x^{2}\)

(ii) \(2x - 3\)

(iii) \(-\dfrac{2}{x^{3}}\)

(iv) \(-\dfrac{2}{(x-1)^{2}}\)

Question. 5

For the function

\(f(x)=\dfrac{x^{100}}{100}+\dfrac{x^{99}}{99}+\cdots+\dfrac{x^{2}}{2}+x+1\),

prove that \(f'(1)=100f'(0)\).

Answer:

Result: \(f'(1)=100f'(0)\)

Question. 6

Find the derivative of the expression:

\(x^{n}+ax^{n-1}+a^{2}x^{n-2}+\cdots +a^{n-1}x+a^{n}\)

Answer:

\(nx^{n-1}+a(n-1)x^{n-2}+a^{2}(n-2)x^{n-3}+\cdots +a^{n-1}\)

Question. 7

For some constants \(a\) and \(b\), find the derivative of the following:

(i) \((x-a)(x-b)\)

(ii) \((ax^{2}+b)^{2}\)

(iii) \(\dfrac{x-a}{x-b}\)

Answer:

(i) \(2x - a - b\)

(ii) \(4ax(ax^{2}+b)\)

(iii) \(\dfrac{a-b}{(x-b)^{2}}\)

Question. 8

Find the derivative of

\(\dfrac{x^{n}-a^{n}}{x-a}\)

for constant \(a\).

Answer:

\(\dfrac{nx^{n}-anx^{n-1}-x^{n}+a^{n}}{(x-a)^{2}}\)

Question. 9

Find the derivative of the following:

(i) \(2x - \dfrac{3}{4}\)

(ii) \((5x^{3}+3x-1)(x-1)\)

(iii) \(x^{-3}(5+3x)\)

(iv) \(x^{5}(3-6x^{-9})\)

(v) \(x^{-4}(3-4x^{-5})\)

(vi) \(\dfrac{2}{x+1} - \dfrac{x^{2}}{3x-1}\)

Answer:

(i) 2

(ii) \(20x^{3} - 15x^{2} + 6x - 4\)

(iii) \(-\dfrac{3}{x^{4}}(5+2x)\)

(iv) \(15x^{4} + \dfrac{24}{x^{5}}\)

(v) \(-\dfrac{12}{x^{5}} + \dfrac{36}{x^{10}}\)

(vi) \(-\dfrac{2}{(x+1)^{2}} - \dfrac{x(3x-2)}{(3x-1)^{2}}\)

Question. 10

Find the derivative of \(\cos x\) from first principle.

Answer:

-\sin x

Question. 11

Find the derivative of the following functions:

(i) \(\sin x \cos x\)

(ii) \(\sec x\)

(iii) \(5\sec x + 4\cos x\)

(iv) \(\csc x\)

(v) \(3\cot x + 5\cosec x\)

(vi) \(5\sin x - 6\cos x + 7\)

(vii) \(2\tan x - 7\sec x\)

Answer:

(i) \(\cos 2x\)

(ii) \(\sec x \tan x\)

(iii) \(5\sec x \tan x - 4\sin x\)

(iv) \(-\csc x \cot x\)

(v) \(-3\csc^{2}x - 5\csc x \cot x\)

(vi) \(5\cos x + 6\sin x\)

(vii) \(2\sec^{2}x - 7\sec x \tan x\)

NCERT Solutions Class 11 – Mathematics – Chapter 12: LIMITS AND DERIVATIVES – EXERCISE 12.2 | Detailed Answers