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CBSE - Class 12 Mathematics Continuity and Differentiability Worksheet
EXERCISE 5.4
Worksheet Answers
Solution:
To differentiate the function $f(x) = \dfrac{e^x}{\sin x}$ with respect to $x$, we identify the form as a quotient of two differentiable functions, $u(x) = e^x$ and $v(x) = \sin x$. [By the Quotient Rule of Differentiation, $\frac{d}{dx} \left[ \frac{u(x)}{v(x)} \right] = \frac{v(x) \cdot u'(x) - u(x) \cdot v'(x)}{[v(x)]^2}$].
Substituting the variables into the Quotient Rule formula:
$\frac{d}{dx} \left( \frac{e^x}{\sin x} \right) = \frac{(\sin x) \cdot \frac{d}{dx}(e^x) - (e^x) \cdot \frac{d}{dx}(\sin x)}{(\sin x)^2}$
Substitute the derivatives found in Step 2 into the equation:
$\frac{d}{dx} \left( \frac{e^x}{\sin x} \right) = \frac{(\sin x)(e^x) - (e^x)(\cos x)}{\sin^2 x}$
Factor out the common term $e^x$ from the numerator:
$\frac{d}{dx} \left( \frac{e^x}{\sin x} \right) = \frac{e^x (\sin x - \cos x)}{\sin^2 x}$
The expression can be left in the consolidated form or expanded as follows:
$\frac{e^x \sin x}{\sin^2 x} - \frac{e^x \cos x}{\sin^2 x} = \frac{e^x}{\sin x} - \frac{e^x \cos x}{\sin^2 x}$
Using trigonometric identities ($\csc x = \frac{1}{\sin x}$ and $\cot x = \frac{\cos x}{\sin x}$):
$\frac{d}{dx} \left( \frac{e^x}{\sin x} \right) = e^x \csc x - e^x \csc x \cot x = e^x \csc x (1 - \cot x)$
Final Solution: $\frac{e^x(\sin x - \cos x)}{\sin^2 x}$ or $e^x \csc x (1 - \cot x)$
Solution:
To differentiate the composite function $f(x) = \sin(\tan^{-1}(e^{-x}))$, we apply the Chain Rule of differentiation. The Chain Rule states that for a composite function $y = f(g(h(x)))$, the derivative is given by:
$\frac{dy}{dx} = \frac{dy}{du} \cdot \frac{du}{dv} \cdot \frac{dv}{dx}$
[Per the Chain Rule of Differentiation]
Let $y = \sin(u)$, where $u = \tan^{-1}(v)$, and $v = e^{-x}$. We differentiate each layer sequentially:
Substituting the variables back into the derivative expression:
$\frac{dy}{dx} = \cos(\tan^{-1}(e^{-x})) \cdot \frac{1}{1 + (e^{-x})^2} \cdot (-e^{-x})$
Simplifying the denominator: $(e^{-x})^2 = e^{-2x}$.
$\frac{dy}{dx} = \frac{-e^{-x} \cos(\tan^{-1}(e^{-x}))}{1 + e^{-2x}}$
To express $\cos(\tan^{-1}(e^{-x}))$ in algebraic form, let $\theta = \tan^{-1}(e^{-x})$, which implies $\tan \theta = e^{-x} = \frac{e^{-x}}{1}$.
Based on the triangle, the hypotenuse is $\sqrt{1^2 + (e^{-x})^2} = \sqrt{1 + e^{-2x}}$. Thus, $\cos \theta = \frac{\text{adjacent}}{\text{hypotenuse}} = \frac{1}{\sqrt{1 + e^{-2x}}}$.
Substitute $\cos(\tan^{-1}(e^{-x})) = \frac{1}{\sqrt{1 + e^{-2x}}}$ into the expression from Step 3:
$\frac{dy}{dx} = \frac{-e^{-x}}{1 + e^{-2x}} \cdot \frac{1}{\sqrt{1 + e^{-2x}}}$
$\frac{dy}{dx} = \frac{-e^{-x}}{(1 + e^{-2x})^{3/2}}$
Final Solution: $\frac{dy}{dx} = \frac{-e^{-x}}{(1 + e^{-2x})^{3/2}}$
Solution:
Let the given function be represented by $y(x)$:
$y = e^x + e^{x^2} + e^{x^3} + e^{x^4} + e^{x^5}$
To find the derivative $\frac{dy}{dx}$, we apply the Sum Rule of differentiation, which states that the derivative of a sum of functions is the sum of their individual derivatives [Per the Linearity of the Differentiation Operator]:
$\frac{dy}{dx} = \frac{d}{dx}(e^x) + \frac{d}{dx}(e^{x^2}) + \frac{d}{dx}(e^{x^3}) + \frac{d}{dx}(e^{x^4}) + \frac{d}{dx}(e^{x^5})$
For composite functions of the form $e^{f(x)}$, we apply the Chain Rule [By the Chain Rule: $\frac{d}{dx}(e^{u}) = e^u \cdot \frac{du}{dx}$]:
Substituting the results from Step 3 back into the summation expression:
$\frac{dy}{dx} = e^x + 2x e^{x^2} + 3x^2 e^{x^3} + 4x^3 e^{x^4} + 5x^4 e^{x^5}$
Final Solution: $\frac{dy}{dx} = e^x + 2x e^{x^2} + 3x^2 e^{x^3} + 4x^3 e^{x^4} + 5x^4 e^{x^5}$
Solution:
Let the given function be denoted as $y$:
$y = \log(\cos e^x)$
To differentiate this function with respect to $x$, we must apply the Chain Rule of differentiation, which states that for a composite function $f(g(h(x)))$, the derivative is $f'(g(h(x))) \cdot g'(h(x)) \cdot h'(x)$. [Per the Chain Rule of Differentiation]
We decompose the function into three distinct nested functions:
Applying the derivative $\frac{dy}{dx} = \frac{dy}{du} \cdot \frac{du}{dv} \cdot \frac{dv}{dx}$:
1. Derivative of outer function: $\frac{d}{du}(\log u) = \frac{1}{u}$
2. Derivative of middle function: $\frac{d}{dv}(\cos v) = -\sin v$
3. Derivative of inner function: $\frac{d}{dx}(e^x) = e^x$ [Per the standard derivative formula for exponential functions]
Substituting the components back into the product chain:
$\frac{dy}{dx} = \frac{1}{\cos(e^x)} \cdot (-\sin(e^x)) \cdot \frac{d}{dx}(e^x)$
$\frac{dy}{dx} = \frac{1}{\cos(e^x)} \cdot (-\sin(e^x)) \cdot e^x$
We observe the term $\frac{\sin(e^x)}{\cos(e^x)}$, which is defined as $\tan(e^x)$ [Per the quotient identity $\tan \theta = \frac{\sin \theta}{\cos \theta}$]:
$\frac{dy}{dx} = - \left( \frac{\sin(e^x)}{\cos(e^x)} \right) \cdot e^x$
$\frac{dy}{dx} = -e^x \tan(e^x)$
Final Solution: $\frac{dy}{dx} = -e^x \tan(e^x)$
Solution:
We are required to find the derivative of the function $f(x)$ with respect to $x$, where:
$f(x) = \frac{\cos x}{\log x}$
Given the condition $x > 0$ and $x \neq 1$ (since $\log 1 = 0$, which would make the denominator undefined), we apply the calculus of quotients.
To differentiate a quotient of two functions $u(x)$ and $v(x)$, we employ the Quotient Rule [Calculus: Differentiation of Quotients]:
$\frac{d}{dx} \left[ \frac{u(x)}{v(x)} \right] = \frac{v(x) \cdot u'(x) - u(x) \cdot v'(x)}{[v(x)]^2}$
Here, let:
Substituting the identified components into the quotient rule expression:
$\frac{d}{dx} \left( \frac{\cos x}{\log x} \right) = \frac{(\log x) \cdot \frac{d}{dx}(\cos x) - (\cos x) \cdot \frac{d}{dx}(\log x)}{(\log x)^2}$
Executing the derivatives determined in Step 1:
$\frac{dy}{dx} = \frac{(\log x)(-\sin x) - (\cos x)(\frac{1}{x})}{(\log x)^2}$
To eliminate the complex fraction in the numerator, we multiply the numerator and denominator by $x$:
$\frac{dy}{dx} = \frac{-x \sin x \log x - \cos x}{x(\log x)^2}$
Factoring out the negative sign from the numerator for clarity:
$\frac{dy}{dx} = -\frac{x \sin x \log x + \cos x}{x(\log x)^2}$
Final Solution: $\frac{d}{dx} \left( \frac{\cos x}{\log x} \right) = -\frac{x \sin x \log x + \cos x}{x(\log x)^2}$
Solution:
Let the given function be defined as $y = f(x)$:
$y = \log(\log x)$
The domain is given as $x > 1$. Since $\log x$ must be positive for the outer logarithm to be defined, we require $\log x > 0$, which implies $x > 1$. This satisfies the existence condition of the composite function [Per the definition of logarithmic domain constraints].
To differentiate a composite function of the form $f(g(x))$, we use the Chain Rule [By the Chain Rule of Differentiation]:
$\frac{dy}{dx} = \frac{d}{dx} [\log(\log x)]$
Let $u = \log x$. Then the expression becomes $y = \log(u)$.
According to the chain rule, $\frac{dy}{dx} = \frac{dy}{du} \cdot \frac{du}{dx}$.
First, differentiate the outer function with respect to $u$ [Using the standard derivative formula $\frac{d}{dx}(\log x) = \frac{1}{x}$]:
$\frac{dy}{du} = \frac{d}{du}(\log u) = \frac{1}{u}$
Second, differentiate the inner function $u$ with respect to $x$:
$\frac{du}{dx} = \frac{d}{dx}(\log x) = \frac{1}{x}$
Substitute the derivatives back into the chain rule product:
$\frac{dy}{dx} = \left( \frac{1}{u} \right) \cdot \left( \frac{1}{x} \right)$
Replace $u$ with its original definition in terms of $x$ ($u = \log x$):
$\frac{dy}{dx} = \frac{1}{\log x} \cdot \frac{1}{x}$
$\frac{dy}{dx} = \frac{1}{x \log x}$
Final Solution: $\frac{dy}{dx} = \frac{1}{x \log x}$
Solution:
Given the function $y = e^{x^3}$, we identify this as a composite function of the form $f(g(x))$, where:
[By the Chain Rule of differentiation, $\frac{d}{dx}[f(g(x))] = f'(g(x)) \cdot g'(x)$]
To differentiate $y = e^{x^3}$ with respect to $x$, we apply the differentiation operator $\frac{d}{dx}$ to both sides:
$\frac{dy}{dx} = \frac{d}{dx}(e^{x^3})$
First, differentiate the outer exponential function with respect to the exponent $x^3$, which yields the exponential function itself [Since $\frac{d}{du}(e^u) = e^u$]:
$\frac{dy}{dx} = e^{x^3} \cdot \frac{d}{dx}(x^3)$
Now, compute the derivative of the inner function $x^3$ using the Power Rule [$\frac{d}{dx}(x^n) = nx^{n-1}$]:
$\frac{d}{dx}(x^3) = 3x^{3-1} = 3x^2$
Substitute the result from Step 3 back into the expression derived in Step 2:
$\frac{dy}{dx} = e^{x^3} \cdot (3x^2)$
Rearranging the terms for standard mathematical notation:
$\frac{dy}{dx} = 3x^2 e^{x^3}$
Final Solution: \frac{dy}{dx} = 3x^2 e^{x^3}
Solution:
The given function is a composite function of the form $y = f(g(x))$, where $f(u) = \cos(u)$ and $u = g(x) = \log x + e^x$. To differentiate this, we must employ the Chain Rule of Differentiation [Per the Chain Rule: $\frac{d}{dx}[f(g(x))] = f'(g(x)) \cdot g'(x)$].
Let $y = \cos(\log x + e^x)$. We differentiate with respect to $x$:
$\frac{dy}{dx} = \frac{d}{dx} [\cos(\log x + e^x)]$
Applying the derivative of the outer function $\cos(u)$, which is $-\sin(u)$:
$\frac{dy}{dx} = -\sin(\log x + e^x) \cdot \frac{d}{dx} (\log x + e^x)$ [By the Chain Rule]
We now differentiate the inner expression $(\log x + e^x)$ term-by-term using the Sum Rule of Differentiation [Per the Sum Rule: $\frac{d}{dx}[u + v] = \frac{du}{dx} + \frac{dv}{dx}$]:
Therefore:
$\frac{d}{dx} (\log x + e^x) = \left( \frac{1}{x} + e^x \right)$
Substituting the result from Step 3 into the equation from Step 2:
$\frac{dy}{dx} = -\sin(\log x + e^x) \cdot \left( \frac{1}{x} + e^x \right)$
Rearranging the terms for mathematical standard form:
$\frac{dy}{dx} = -\left( \frac{1}{x} + e^x \right) \sin(\log x + e^x)$
Final Solution: $\frac{dy}{dx} = -\left( \frac{1 + x e^x}{x} \right) \sin(\log x + e^x)$
Solution:
Let the given function be represented as $y$:
$y = e^{\sin^{-1} x}$
[Definition of the function for differentiation]
To differentiate this function, we employ the Chain Rule of calculus. Since the function is a composite function of the form $f(g(x))$, where $f(u) = e^u$ and $g(x) = \sin^{-1} x$, the derivative is given by:
$\frac{dy}{dx} = \frac{d}{du}(e^u) \cdot \frac{d}{dx}(\sin^{-1} x)$
[Per the Chain Rule for differentiation]
Applying the standard derivative formulas for the exponential function and the inverse trigonometric function:
1. The derivative of $e^u$ with respect to $u$ is $e^u$.
2. The derivative of $\sin^{-1} x$ with respect to $x$ is $\frac{1}{\sqrt{1 - x^2}}$.
[Standard derivatives: $\frac{d}{dx}e^x = e^x$ and $\frac{d}{dx}(\sin^{-1} x) = \frac{1}{\sqrt{1-x^2}}$]
Substituting the derivatives back into the Chain Rule expression:
$\frac{dy}{dx} = e^{\sin^{-1} x} \cdot \frac{d}{dx}(\sin^{-1} x)$
$\frac{dy}{dx} = e^{\sin^{-1} x} \cdot \left( \frac{1}{\sqrt{1 - x^2}} \right)$
Combining the terms into a single rational expression:
$\frac{dy}{dx} = \frac{e^{\sin^{-1} x}}{\sqrt{1 - x^2}}$
[Subject to the domain constraint $|x| < 1$ for the derivative to be defined]
Final Solution: $\frac{dy}{dx} = \frac{e^{\sin^{-1} x}}{\sqrt{1 - x^2}}$
Solution:
Let the given function be defined as:
$y = \sqrt{e^{\sqrt{x}}}$
Rewrite the function using exponential notation to facilitate differentiation:
$y = (e^{\sqrt{x}})^{1/2} = e^{\frac{1}{2}\sqrt{x}}$ [By Law of Exponents: $(a^m)^n = a^{mn}$]
To differentiate $y$ with respect to $x$, we apply the Chain Rule, which states that for a composite function $f(g(x))$, the derivative is $f'(g(x)) \cdot g'(x)$. [Per the Chain Rule of Calculus].
Let $u = \frac{1}{2}\sqrt{x} = \frac{1}{2}x^{1/2}$. Then $y = e^u$.
$\frac{dy}{dx} = \frac{dy}{du} \cdot \frac{du}{dx}$
Part A: Differentiation of the exponential term
$\frac{d}{du}(e^u) = e^u$ [Standard derivative formula for exponential functions].
Substituting $u$ back, we get: $e^{\frac{1}{2}\sqrt{x}}$.
Part B: Differentiation of the exponent term
$\frac{d}{dx}\left(\frac{1}{2}x^{1/2}\right) = \frac{1}{2} \cdot \frac{d}{dx}(x^{1/2})$
Using the Power Rule $\frac{d}{dx}(x^n) = nx^{n-1}$:
$\frac{1}{2} \cdot \left(\frac{1}{2}x^{1/2 - 1}\right) = \frac{1}{4}x^{-1/2} = \frac{1}{4\sqrt{x}}$
Multiplying the results from Part A and Part B:
$\frac{dy}{dx} = e^{\frac{1}{2}\sqrt{x}} \cdot \frac{1}{4\sqrt{x}}$
Substitute $e^{\frac{1}{2}\sqrt{x}}$ back to the original radical form $\sqrt{e^{\sqrt{x}}}$:
$\frac{dy}{dx} = \frac{\sqrt{e^{\sqrt{x}}}}{4\sqrt{x}}$
Final Solution: $\frac{dy}{dx} = \frac{\sqrt{e^{\sqrt{x}}}}{4\sqrt{x}}$