Mathematics and Statistics · Class 12 Commerce
Ch 4Applications of Derivatives — Class 12 Mathematics and Statistics, concept-first.
Once we can differentiate a function, the derivative becomes a powerful tool for describing how the function behaves — whether its values are rising or falling, where it turns, and where it reaches a largest or smallest value.
Key concepts
Hover a concept to preview it and jump to its most relevant Q&A.
Increasing and Decreasing Functions
A function is (strictly/monotonically) increasing on an interval if, whenever in that interval, ; it is decreasing if whenever .
Most relevant Q&A
- Show that the function $f(x) = 4x^3 - 18x^2 + 27x - 7$ is increasing for all real $x$.Free
- A differentiable function $f$ is strictly increasing on an interval $I$ if, for every $x$ in $I$: (a) $f'(x) < 0$ (b) $f'(x) > 0$ (c) $f'(x)…Preview
- Find the intervals on which $f(x) = x^3 - 6x^2 + 9x + 15$ is increasing and those on which it is decreasing.Free
- State whether the following statement is true or false. If $f'(x) > 0$ for all $x \in (a, b)$ then $f(x)$ is decreasing function in the inte…Preview
- A function f is said to be increasing at a point c if ______. (a) $f'(c) = 0$ (b) $f'(c) > 0$ (c) $f'(c) < 0$ (d) $f'(c) = 1$Preview
Chapter contents
The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.
Increasing and Decreasing Functions
Once we can differentiate a function, the derivative becomes a powerful tool for describing how the function behaves — whether its values are rising or falling, where it turns, and where it reaches a…
Maxima and Minima — The First Derivative Test
A point where a function stops rising and begins to fall (or stops falling and begins to rise) is of special interest: it is where the function attains a local maximum or a local minimum.
The Second Derivative Test
The first derivative test works in every case, but it requires checking the sign of on both sides of each critical point.
Cost, Revenue and Marginal Analysis
The most direct commercial use of the derivative is marginal analysis — measuring the effect on cost, revenue or profit of producing or selling one more unit.
Elasticity of Demand
Demand for a good depends on its price: usually, the higher the price , the smaller the quantity demanded .
Optimisation in Commerce — Maximising Profit and Minimising Cost
The techniques of maxima and minima (Sections 2–3) combine with the cost–revenue functions (Section 4) to answer the questions a business most wants answered: what output maximises profit? and what ou…
Exercises
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- Q9Show that the function $f(x) = 4x^3 - 18x^2 + 27x - 7$ is increasing for all real $x$.Free
- Q10Find the local maximum and local minimum values of $f(x) = x^3 - 9x^2 + 24x - 12$ using the second derivative test.Free
- Q11The demand function is $x = 40 - 5p$, where $x$ is the quantity demanded at price $p$ (in ₹). Find the elasticity of demand at $p = 6$ and i…Free
- Q12The demand function is $p = 40 - 2x$ (price in ₹ when $x$ units are sold). Find the number of units that maximises the total revenue, and th…Preview
- Q13A differentiable function $f$ is strictly increasing on an interval $I$ if, for every $x$ in $I$: (a) $f'(x) < 0$ (b) $f'(x) > 0$ (c) $f'(x)…Preview
- Q14The total cost of producing $x$ units is $C(x) = 3x^2 + 12x + 75$ (in ₹). Find the output at which the average cost is minimum and the minim…Preview
- Q15A company's demand function is $p = 80 - x$ (price in ₹ per unit) and its total cost is $C(x) = 100 + 30x$. Determine the output that maximi…Preview
Sample & Board Papers
Sample papers and previous-year board questions for this subject.
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- Q1State whether the following statement is true or false. If $f'(x) > 0$ for all $x \in (a, b)$ then $f(x)$ is decreasing function in the inte…Preview
- Q2Divide 20 into two ports, so that their product is maximum.Preview
- Q3Complete the following activity to find MPC, MPS, APC and APS, if the expenditure $E_c$ of a person with income $I$ is given as: $E_c = (0.0…Preview
- Q4A function f is said to be increasing at a point c if ______. (a) $f'(c) = 0$ (b) $f'(c) > 0$ (c) $f'(c) < 0$ (d) $f'(c) = 1$Preview
- Q5If $0 < \eta < 1$ then the demand is ______.Preview
- Q6For manufacturing x units, labour cost is $150 - 54x$ and processing cost is $x^2$. Price of each unit is $p = 10800 - 4x^2$. Find the value…Preview
- Q7For manufacturing x units, labour cost is $150 - 54x$ and processing cost is $x^2$. Price of each unit is $p = 10800 - 4x^2$. Find the value…Preview
- Q8A rod of 108 m long is bent to form a rectangle. Find it’s dimensions when it’s area is maximum.Preview
- Q9The slope of tangent at any point $(a, b)$ is also called as ______.Preview
- Q10Determine the minimum value of the function. $f(x) = 2x^3 - 21x^2 + 36x - 20$Preview
- Q11The consumption expenditure $E_c$ of a person with the income $x$. is given by $E_c = 0.0006x^2 + 0.003x$. Find MPC, MPS, APC and APS when t…Preview
- Q12The average revenue $R_A$ is 50 and elasticity of demand $\eta$ is 5, the marginal revenue $R_M$ is ______.Preview
- Q13Find MPC, MPS, APC and APS, if the expenditure $E_c$ of a person with income I is given as $E_c = (0.0003) I^2 + (0.075) I$ ; When $I = 1000…Preview
- Q14Divide the number 84 into two parts such that the product of one part and square of the other is maximum. Solution: Let one part be x then t…Preview
- Q15The equation of normal to the curve $y = 3x^2 - x + 1$ at $(1, 3)$ is ______. (a) $x - 5y - 16 = 0$ (b) $x + 5y - 16 = 0$ (c) $x - 5y + 16 =…Preview
- Q16If $f(x) = x \cdot \log x$ then its minimum value is ______.Preview
- Q17The consumption expenditure $E_c$ of a person with the income $x$. is given by $E_c = 0.0006x^2 + 0.003x$. Find MPC, MPS, APC and APS when t…Preview
- Q18If the demand function is $D = 50 - 3p - p^2$. Find the elasticity of demand at $p = 5$ comment on the result.Preview
- Q19Find the values of $x$ for which $f(x) = 3x^2 - 15x + 9$ is decreasing.Preview
- Q20Find MPC, MPS, APC and APS, if the expenditure $E_c$ of a person with his income $I$ is given as $E_c = (0.0003)I^2 + (0.075)I$, when $I = 1…Preview
- Q21A manufacturer can sell $x$ items at a price of ₹$(280 - x)$ each. The cost of producing $x$ items is ₹$(x^2 + 40x + 35)$. Find the number o…Preview
More questions
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- Example 1Find the intervals on which $f(x) = x^3 - 6x^2 + 9x + 15$ is increasing and those on which it is decreasing.Free
- Example 2Using the first derivative test, find the local maximum and local minimum values of $f(x) = x^3 - 3x + 2$.Free
- Example 3Using the second derivative test, find the local extreme values of $f(x) = 2x^3 - 15x^2 + 36x + 10$.Free
- Example 4The total cost (in ₹) of producing $x$ units of a product is $C(x) = x^3 - 6x^2 + 15x + 50$. Find the average cost and the marginal cost whe…Preview
- Example 5The demand function for a commodity is $p = 25 - 2x$, where $p$ is the price per unit (in ₹) when $x$ units are demanded. Find the total rev…Preview
- Example 6The demand for a good is $x = 20 - 2p$, where $x$ is the quantity demanded at price $p$ (in ₹). Find the elasticity of demand at $p = 4$ and…Preview
- Example 7A firm faces the demand $p = 50 - x$ (price in ₹ when $x$ units are sold) and total cost $C(x) = 100 + 20x$. Find the output that maximises…Preview
- Example 8The total cost of producing $x$ units is $C(x) = x^2 + 40x + 400$ (in ₹). Find the output at which the average cost is minimum, and show tha…Preview