Question

Use the reduction formulas in a table of integrals to evaluate the following integrals. $$\int \sec ^{4} 4 x d x$$

Short answer

Question: Evaluate the integral $$\int \sec^4(4x) dx$$. Answer: The integral of the given function is $$\int \sec^4(4x) dx = \frac{\sec^2(4x) \tan(4x)}{3} + \frac{1}{2}\tan(4x) + C$$, where C is the constant of integration.

Step-by-step solution

Identify the reduction formula for even powers of secant function

The reduction formula for even powers of secant function is given by the formula: $$\int \sec^n(x) dx = \frac{1}{n-1} \sec^{n-2}(x) \tan(x) + \frac{n-2}{n-1}\int \sec^{n-2}(x) dx$$ Where n is an even integer.

Apply the reduction formula to the given integral

We are given the integral: $$\int \sec^4(4x) dx$$ Here, we have \(n=4\), and the function inside the secant is \(4x\). Applying the reduction formula, we get: $$\int \sec^4(4x) dx = \frac{1}{4-1} \sec^2(4x) \tan(4x) + \frac{4-2}{4-1}\int \sec^2(4x) dx$$ Simplify the expression: $$\int \sec^4(4x) dx = \frac{\sec^2(4x) \tan(4x)}{3} + \frac{2}{3}\int \sec^2(4x) dx$$

Evaluate the remaining integral

Now, we need to evaluate the integral of \(\sec^2(4x)\). This integral is a standard one and can be easily recognized as the derivative of the tangent function. Thus, we have: $$\int \sec^2(4x) dx = \tan(4x) + C$$ However, since we have a chain rule in action (\(u=4x\)), we need to apply the substitution rule and divide by the derivative of \(u\), which is \(4\): $$\int \sec^2(4x) dx = \frac{1}{4}(\tan(4x) + C)$$

Substitute the result back into the original expression

Now, substitute the result of the remaining integral back into the expression obtained in Step 2: $$\int \sec^4(4x) dx = \frac{\sec^2(4x) \tan(4x)}{3} + \frac{2}{3}\left(\frac{1}{4}(\tan(4x) + C)\right)$$ Simplify the expression: $$\int \sec^4(4x) dx = \frac{\sec^2(4x) \tan(4x)}{3} + \frac{1}{2}\tan(4x) + \frac{2}{12}C$$

Write down the final answer

The integral of the given function is: $$\int \sec^4(4x) dx = \frac{\sec^2(4x) \tan(4x)}{3} + \frac{1}{2}\tan(4x) + C$$ Where C is the constant of integration.

Key concepts

Integration

Integration is a fundamental concept in calculus used to find areas under curves and sums of continuous functions over intervals. It is essentially the reverse process of differentiation.
The integral of a function gives us the accumulation of quantities and can be deemed as a measure of total change.
Integrals can be classified mainly into two types:

• Definite integrals – Used when computing areas under the curve from one point to another.
• Indefinite integrals – Express the general form of the antiderivative, without specific bounds.

In our exercise, we are focused on indefinite integrals related to trigonometric functions.
By using specific techniques like reduction formulas, we can handle complex integrals involving powers of trigonometric functions like the secant function.

Trigonometric Integrals

Trigonometric integrals involve functions of angles or ratios of lengths in right-angled triangles. These integrals often include sine, cosine, tangent, and secant functions.
Trigonometric integrals are crucial in various fields such as physics and engineering. Reduction formulas help simplify trigonometric integrals, especially when dealing with powers of these functions.
This can reduce the complexity significantly when integrating powers higher than two.
In the given problem, we work with \(\sec^4(4x)\).
Utilizing the reduction formula, we transform this into a sum of simpler integrals that are easier to solve. This method saves time and simplifies complex expressions in calculus.

Secant Function

The secant function, denoted as sec(x), is one of the primary trigonometric functions. It is the reciprocal of the cosine function and has significant roles when dealing with integrals of trigonometric expressions.
The properties of the secant function often allow it to appear in problems involving integration because of its distinct behavior.Key properties include:

• Secant function is defined as \( \sec(x) = \frac{1}{\cos(x)} \).
• Its graph has vertical asymptotes at points where cosine is zero.
• It has a period of \(2\pi\).

When using the reduction formula for integrals, the secant function's powers can be reduced systematically, making integration more approachable.

Chain Rule

The chain rule is a fundamental differentiation rule used to compute the derivative of functions composed of other functions. When an integral involves a composite function, the chain rule helps express it in a solvable form.For example, in the given integral \( \int \sec^2(4x) dx \), the chain rule applies because the function inside the trigonometric expression is \(4x\).
When differentiating or integrating a composite function f(g(x)), the derivative is found by multiplying the derivative of f with respect to g by the derivative of g with respect to x.Steps involved include:

• Identify the inner function, in this case, \(u = 4x\).
• Integrate using known identities, then adjust for the derivative of the inner function, \(\frac{1}{4}\), which corrects for the change of variable technique.

Using the chain rule correctly simplifies the integration process and ensures accurate results, as seen in how we adjusted the integral of \[ \int \sec^2(4x) dx \] in the problem.