Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 11

Tan (2x + 1) - Mathematics

tan (2x + 1)

Solution

$\frac{d}{dx}\left( f(x) \right) = \lim_{h \to 0} \frac{f\left( x + h \right) - f\left( x \right)}{h}$
$= \lim_{h \to 0} \frac{\tan \left( 2x + 2h + 1 \right) - \tan \left( 2x + 1 \right)}{h}$
$= \lim_{h \to 0} \frac{\frac{sin \left( 2x + 2h + 1 \right)}{\cos \left( 2x + 2h + 1 \right)} - \frac{\sin \left( 2x + 1 \right)}{\cos \left( 2x + 1 \right)}}{h}$
$= \lim_{h \to 0} \frac{sin \left( 2x + 2h + 1 \right) \cos \left( 2x + 1 \right) - \cos \left( 2x + 2h + 1 \right) \sin \left( 2x + 1 \right)}{h \cos \left( 2x + 2h + 1 \right) \cos \left( 2x + 1 \right)}$
$= \lim_{h \to 0} \frac{\sin \left( 2x + 2h + 1 - 2x - 1 \right)}{h \cos \left( 2x + 2h + 1 \right) \cos \left( 2x + 1 \right)}$
$= \frac{1}{\cos \left( 2x + 1 \right)} \lim_{h \to 0} \frac{\sin \left( 2h \right)}{2h} \times 2 \lim_{h \to 0} \frac{1}{\cos \left( 2x + 2h + 1 \right)}$
$= \frac{1}{\cos \left( 2x + 1 \right)} \times 2 \times \frac{1}{\cos \left( 2x + 1 \right)}$
$= \frac{2}{\cos^2 \left( 2x + 1 \right)}$
$= 2 \sec^2 \left( 2x + 1 \right)$

Concept: The Concept of Derivative - Algebra of Derivative of Functions
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APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 30 Derivatives
Exercise 30.2 | Q 4.2 | Page 26