CBSE Class 12 Mathematics Derivatives Q #1268
COMPETENCY BASED
UNDERSTAND
2 Marks 2024 AISSCE(Board Exam) VSA
If $f(x)=|tan~2x|$, then find the value of $f^{\prime}(x)$ at $x=\frac{\pi}{3}$

AI Tutor Explanation

Powered by Gemini

Detailed Solution

Step 1: Analyze the function

Given $f(x) = |\tan 2x|$. We need to find $f'(x)$ at $x = \frac{\pi}{3}$. First, we need to determine if $\tan 2x$ is positive or negative at $x = \frac{\pi}{3}$.

Step 2: Determine the sign of tan(2x) at x = pi/3

At $x = \frac{\pi}{3}$, $2x = \frac{2\pi}{3}$. Since $\frac{2\pi}{3}$ is in the second quadrant, $\tan \frac{2\pi}{3}$ is negative. Therefore, $\tan 2x < 0$ at $x = \frac{\pi}{3}$.

Step 3: Rewrite the function without absolute value

Since $\tan 2x < 0$ at $x = \frac{\pi}{3}$, we can rewrite $f(x)$ as $f(x) = -\tan 2x$ in a neighborhood around $x = \frac{\pi}{3}$.

Step 4: Differentiate the function

Now, we differentiate $f(x) = -\tan 2x$ with respect to $x$: $$f'(x) = -\frac{d}{dx}(\tan 2x) = -(\sec^2 2x) \cdot 2 = -2\sec^2 2x$$

Step 5: Evaluate the derivative at x = pi/3

Now, we evaluate $f'(x)$ at $x = \frac{\pi}{3}$: $$f'\left(\frac{\pi}{3}\right) = -2\sec^2\left(2 \cdot \frac{\pi}{3}\right) = -2\sec^2\left(\frac{2\pi}{3}\right)$$ Since $\sec\left(\frac{2\pi}{3}\right) = \frac{1}{\cos\left(\frac{2\pi}{3}\right)} = \frac{1}{-\frac{1}{2}} = -2$, we have: $$f'\left(\frac{\pi}{3}\right) = -2(-2)^2 = -2(4) = -8$$

Final Answer: -8

AI generated content. Review strictly for academic accuracy.

Pedagogical Audit
Bloom's Analysis: This is an UNDERSTAND question because the student needs to understand the properties of absolute value functions and trigonometric functions to correctly differentiate the given function. They must also understand in which quadrant the angle lies to determine the sign of the trigonometric function.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the student to apply the rules of differentiation to a trigonometric function involving an absolute value. This involves a series of steps, including determining the sign of the function inside the absolute value, rewriting the function, and then applying the chain rule.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. The question assesses the student's ability to apply the concepts of differentiation and trigonometric functions in a problem-solving context, requiring them to analyze the function and choose the correct approach.

More from this Chapter

SA
If $x\sqrt{1+y}+y\sqrt{1+x}=0$, $-1
MCQ_SINGLE
The derivative of \(\tan^{-1}(x^{2})\) w.r.t. x is :
SA
Find $\frac{dy}{dx}$ , if $(cos~x)^{y}=(cos~y)^{x}.$
SA
Differentiate $y=\cos^{-1}\left(\frac{1-x^{2}}{1+x^{2}}\right)$ with respect to x, when $x\in(0,1)$.
SUBJECTIVE
Amusement parks heavily rely on mathematical curves to design roller coaster tracks, balancing intense thrill with absolute safety. For a safe ride, the track must have no breaks (it must be continuous) and no sharp, sudden corners (it must be differentiable/smooth). An engineering team is designing a transition segment of a new coaster. The height $h(x)$ (in meters) of the track at a horizontal distance $x$ (in meters) from the starting platform is modeled by the following piecewise function: $$h(x) = \begin{cases} \frac{1}{2}x^2 + 2x, & 0 \leq x < 2 \\ ax + b, & 2 \leq x \leq 5 \end{cases}$$ Based on the given information, answer the following questions: (i) For the track to have no broken rails at the transition point $x = 2$, it must be continuous. Formulate the mathematical equation relating $a$ and $b$ to ensure this continuity. (1 Mark) (ii) Find the left-hand derivative (the slope of the track just before the transition point) at $x = 2$. (1 Mark) (iii) To ensure the transition at $x = 2$ is perfectly smooth (differentiable), calculate the exact values of $a$ and $b$ that the engineers must use. (2 Marks) — OR — (iii) If a junior engineer mistakenly designed the second track segment using $a = 3$ and $b = 0$, verify whether the track is mathematically safe (smooth and differentiable) at $x = 2$. Justify your answer. (2 Marks)
View All Questions