Finding the Derivative of Functions

Master derivatives in CBSE Class 11 Applied Mathematics. Learn power rule, sum rule, and product rule with step-by-step solutions and practice problems.

Definition of Derivative

The derivative of a function f(x) measures the instantaneous rate of change of the function with respect to x. It is defined as the limit of the difference quotient as the interval approaches zero. Geometrically, it represents the slope of the tangent line to the curve at any point x.

f'(x) = lim(h→0) [f(x+h) − f(x)] / h
Example: Solved Example: Find the derivative of f(x) = 5
Show Step-by-Step Solution

Step 1: Apply the definition f'(x) = lim(h→0) [f(x+h) − f(x)] / h.
Step 2: Since f(x) = 5, f(x+h) = 5.
Step 3: f'(x) = lim(h→0) [5 − 5] / h = lim(h→0) 0 / h = 0.
Answer: 0

The Power Rule

For any real number n, the derivative of the power function xⁿ is given by multiplying the exponent by the base and subtracting one from the exponent. This is the most fundamental rule for differentiating polynomials. It applies to all integer and fractional powers of x.

d/dx (xⁿ) = n·xⁿ⁻¹
Example: Solved Example: Find the derivative of f(x) = x⁴
Show Step-by-Step Solution

Step 1: Identify n = 4.
Step 2: Apply the formula d/dx (xⁿ) = n·xⁿ⁻¹.
Step 3: f'(x) = 4·x⁴⁻¹ = 4x³.
Answer: 4x³

Sum and Constant Multiple Rules

The derivative of a sum of two functions is the sum of their individual derivatives. Additionally, the derivative of a constant multiplied by a function is the constant times the derivative of the function. These rules allow us to differentiate complex polynomial expressions term by term.

d/dx [c·f(x) + g(x)] = c·f'(x) + g'(x)
Example: Solved Example: Find the derivative of f(x) = 3x² + 2x
Show Step-by-Step Solution

Step 1: Differentiate each term separately.
Step 2: d/dx (3x²) = 3·(2x) = 6x.
Step 3: d/dx (2x) = 2·(1) = 2.
Answer: 6x + 2