Problem 296 - Mathematics for IIT JEE Main and Advanced Differential Calculus Algebra Trigonometry

Question

$$ \text { If } y=x^{3} \sin x, \text { find } y_{20} $$

Step-by-Step Solution

Answer

y_20 = (20)^3 * sin(20) = 8000 * sin(20)

Step 1: Substitute x with 20 in the given function

Replace x with 20 in the given function y = x^3 * sin(x).

Step 2: Calculate y_20

Plug in 20 as the value for x in y = x^3 * sin(x) to find y_20: y_20 = (20)^3 * sin(20).

Key Concepts

Higher Order Derivatives

In calculus, the concept of higher order derivatives plays a critical role in understanding how functions change. A derivative essentially gives you information about the rate of change. The first derivative tells you how a function changes at a single moment in time, but higher order derivatives provide insights into how the rate of change itself changes. For example, the second derivative might tell you about acceleration if the first derivative is about speed.
When dealing with functions like \( y = x^3 \sin x \), finding higher order derivatives involves repeatedly applying differentiation rules. In some problems, you're not just solving for the first derivative but for a derivative at a particular order. If you see \( y_{20} \), it means you're looking at the 20th derivative of \( y \).

• Higher order derivatives can reveal patterns and are used in differential equations and series expansion.
• The process often involves finding simpler forms or repeated patterns in derivatives to make computation feasible.
• They can be practical for approximating functions, analyzing mechanical systems, or understanding oscillations.

Trigonometric Functions

Trigonometric functions such as sine, cosine, and tangent are cornerstone elements in mathematics, particularly in calculus. They describe angles and relationships in triangles but also appear in various applications ranging from engineering to physics.
The function \( \sin x \) in our example \( y = x^3 \sin x \) is a periodic function, meaning it repeats its values in a regular pattern and this behavior profoundly affects how derivatives behave. For derivatives of trigonometric functions:

• The derivative of \( \sin x \) is \( \cos x \).
• The derivative of \( \cos x \) is \( -\sin x \).
• These properties will cycle through as you take higher derivatives.

The periodicity and symmetrical properties of trigonometric functions often simplify the differentiation process. Notably, they're used in Fourier series, which decompose functions into sinusoidal functions, and in solving wave equations.

Product Rule in Differentiation

In differential calculus, the product rule is a fundamental technique used to differentiate products of two functions. It states that if you have two functions \( u(x) \) and \( v(x) \), the derivative of their product \( y = u(x) v(x) \) is given by:
\[ y' = u'(x) v(x) + u(x) v'(x) \]
This rule is vital when functions are multiplied together, as in \( y = x^3 \sin x \). Here:

• \( u(x) = x^3 \) and \( v(x) = \sin x \).
• Applying the product rule, differentiate each function separately.
• Combine these results to find the derivative of the product.

The power of the product rule is that it breaks down a complex function into simpler parts, making it easier to handle. This becomes especially useful when you want to determine higher order derivatives, as it provides a foundation for methods of repeated differentiation.