Application Of Derivatives Class 12 Exam Prep Revision — Grandmaster Guide
Ayush (Founder)
Exam Strategist
- The derivative of a function f(x) is denoted as f'(x) or df/dx
- Geometrically, the derivative represents the slope of the tangent to a curve at a point
- If y = f(x), then dy/dx = f'(x)
- Derivative of xⁿ is nxⁿ⁻¹
- Derivative of s∈ x is cos x
- Derivative of cos x is -s∈ x
- Derivative of tan x is sec²x
- Derivative of eˣ is eˣ
- Derivative of log(x) is 1/x
- For a function y = f(g(x)), the derivative is given by dy/dx = f'(g(x)) * g'(x)
- For a function y = f(x)/g(x), the derivative is given by dy/dx = (f'(x)g(x) - f(x)g'(x)) / g(x)²
- The second derivative of a function f(x) is denoted as f''(x) or d²f/dx²
- If f(x) is a function, then its derivative f'(x) represents the rate of change of the function with respect to x
- Increasing function: f'(x) > 0
- Decreasing function: f'(x) < 0
- Maxima or Minima: f'(x) = 0
- Inflection point: f''(x) = 0
🪤 The 5 Mistakes That Cost Marks
- Not checking the doma∈ of the function before differentiating
- Forgetting to apply the cha∈ rule ∈ composite functions
- Not using the correct formula for the derivative of trigonometric functions
- Not checking for the existence of the derivative at a point
- Not using the second derivative test to determine the nature of the critical points
✏️ 3 Solved PYQs
- Question 1: Find the derivative of the function f(x) = x³ s∈ x
- Solution: Using the product rule, f'(x) = d(x³ s∈ x)/dx = x³ cos x + s∈ x * 3x² = x³ cos x + 3x² s∈ x
- Question 2: Find the equation of the tangent to the curve y = x² + 3x - 2 at the point (1, 2)
- Solution: First, find the derivative of the function y = x² + 3x - 2, which is dy/dx = 2x + 3
- At the point (1, 2), the slope of the tangent is 2*1 + 3 = 5
- The equation of the tangent is y - 2 = 5(x - 1)
- Question 3: Find the maximum value of the function f(x) = x³ - 6x² + 9x + 2
- Solution: First, find the critical points by taking the derivative and equating it to zero
- f'(x) = 3x² - 12x + 9 = 0
- Solving for x, we get x = 1 and x = 3
- Now, use the second derivative test to determine the nature of the critical points
- f''(x) = 6x - 12
- At x = 1, f''(1) = 6 - 12 = -6 < 0, so x = 1 is a local maxima
- At x = 3, f''(3) = 18 - 12 = 6 > 0, so x = 3 is a local minimum
- The maximum value of the function is at x = 1, which is f(1) = 1 - 6 + 9 + 2 = 6
🧠 The One Thing Most Students Get Wrong
- Most students get wrong the application of the cha∈ rule ∈ composite functions
- They often forget to multiply the derivative of the outer function by the derivative of the inner function
- For example, if y = s∈(x²), then dy/dx = cos(x²) * d(x²)/dx = cos(x²) * 2x
- Another common mistake is not using the correct formula for the derivative of trigonometric functions
- For example, the derivative of tan x is sec²x, not tan x
👁️ Ayush's Note
- To solve application of derivatives problems, first identify the type of problem
- If it is a maxima/minima problem, use the first derivative test or the second derivative test
- If it is a tangent equation problem, use the point-slope form of a line
- If it is a rate of change problem, use the concept of related rates
- Always check the doma∈ of the function before differentiating
- Always use the correct formula for the derivative of trigonometric functions
- Practice, practice, practice, as application of derivatives is a topic that requires a lot of practice to master
🔁 Last 5 Minutes Box
- Revision of important formulas and concepts
- Practice of solving problems quickly and efficiently
- Focus on the most common types of problems
- Use of shortcuts and tricks to solve problems quickly
- Stay calm and focused, and try to solve as many problems as possible ∈ the last 5 minutes
📝 Practice MCQs
1. Question: Find the derivative of the function f(x) = x² s∈ x
A) x² cos x + 2x s∈ x
B) x² cos x - 2x s∈ x
C) x² cos x + x s∈ x
D) x² cos x - x s∈ x
Answer: A) x² cos x + 2x s∈ x
2. Question: Find the equation of the tangent to the curve y = x³ - 2x² + x - 1 at the point (1, -1)
A) y + 1 = 2(x - 1)
B) y + 1 = 0(x - 1)
C) y + 1 = -2(x - 1)
D) y + 1 = 1(x - 1)
Answer: C) y + 1 = 0(x - 1)
3. Question: Find the maximum value of the function f(x) = x³ - 3x² + 2x + 1
A) 4
B) 5
C) 6
D) 7
Answer: B) 5
4. Question: Find the derivative of the function f(x) = eˣ s∈ x
A) eˣ s∈ x + eˣ cos x
B) eˣ s∈ x - eˣ cos x
C) eˣ s∈ x + eˣ tan x
D) eˣ s∈ x - eˣ tan x
Answer: A) eˣ s∈ x + eˣ cos x
5. Question: Find the equation of the tangent to the curve y = x² + 2x - 3 at the point (1, 0)
A) y - 0 = 4(x - 1)
B) y - 0 = 2(x - 1)
C) y - 0 = -4(x - 1)
D) y - 0 = -2(x - 1)
Answer: B) y - 0 = 4(x - 1)
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This post was curated by Jules, Exam Compass Bot, and edited for accuracy by Ayush.
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