Question

In Exercises, find the second derivative of the function. $$ f(x)=3 x^{2}+4 x $$

Short answer

The second derivative of function \(f(x) = 3x^2 + 4x\) is \(f''(x) = 6\).

Step-by-step solution

Differentiate the function first time

Since \(f(x) = 3x^2 + 4x\), using the power rule of derivation, which states that the derivative of \(x^n\) is \(nx^{n-1}\), the derivative of \(f(x)\) regarding \(x\) is computed as follows: \(f'(x) = 2*3x^{2-1} + 4*1x^{1-1} = 6x + 4\)

Differentiate the function second time

Next, derive the function \(f'(x) = 6x + 4\). This will give the second derivative \(f''(x)\): Using the power rule of derivation again, \(f''(x) = 6*1x^{1-1} + 4*0x^{0-1} = 6\). The second term vanishes because any number multiplied by zero gives zero.

Key concepts

Second Derivative

The second derivative of a function gives insight into the "acceleration" of the function. Think of it like this: if the first derivative is the speed, the second derivative tells us how that speed is changing. If the second derivative is positive, the function is curving upwards like a smile, indicating that it's concave up. If it is negative, the function looks like a frown, or concave down.

For example, with the function \(f(x) = 3x^2 + 4x\), we first found the initial derivative \(f'(x) = 6x + 4\). To find the second derivative, \(f''(x) = 6\), we differentiated \(6x + 4\) once more. Here, the second derivative is simply 6, which is positive. This tells us that our original function is curving upwards everywhere.

Power Rule

The power rule is a handy shortcut for finding derivatives, especially useful for polynomials. Instead of performing the limit process from first principles, the power rule simplifies things dramatically. It states that if you have a function \(x^n\), its derivative is \(nx^{n-1}\). This means you multiply the power by the coefficient and then reduce the power by one.

In our example with the function \(f(x) = 3x^2 + 4x\):

• For \(3x^2\), apply the power rule: \(2 \times 3x^{2-1} = 6x\)
• For \(4x\), since it's \(x^1\), it becomes \(1 \times 4x^{1-1} = 4\)

Thus, the derivative \(f'(x) = 6x + 4\) was quickly found using the power rule.

Differentiation

Differentiation is the process of finding the derivative of a function, and it's a fundamental concept in calculus. By differentiating a function, you are essentially determining the rate at which the function's value is changing at any given point.

This has a multitude of applications:

• Understanding how a quantity changes over time (like speed over time).
• Finding maxima and minima, which can help in optimizing problems.
• Studying the behavior and shape of graphs.

In our specific exercise, differentiation helped us find both the first and second derivatives. We started with \(f(x) = 3x^2 + 4x\), calculated the first derivative \(f'(x) = 6x + 4\), and then differentiated once more to find the second derivative \(f''(x) = 6\). Each step gave us deeper insights into the behavior of the original function.