Chapter 3: Problem 6
Find the derivatives of the functions. \(\sqrt{625-x^{2}}+3 x^{3}+12\)
Short Answer
Expert verified
The derivative of the function is \( f'(x) = -\frac{x}{\sqrt{625-x^{2}}} + 9x^{2} \).
Step by step solution
01
Identify the Function Components
The function given is \( f(x) = \sqrt{625-x^{2}} + 3x^{3} + 12 \). This function contains three parts: \( \sqrt{625-x^{2}} \), \( 3x^{3} \), and the constant \( 12 \).
02
Differentiate the First Component
To differentiate \( \sqrt{625-x^{2}} \), rewrite it as \( (625-x^{2})^{1/2} \). Use the chain rule: The derivative of \( u^{n} \) is \( nu^{n-1} \cdot u' \). Here, \( u = 625-x^{2} \) and \( n = 1/2 \). So, \( u' = -2x \). The derivative is \(-x(625-x^{2})^{-1/2} \).
03
Differentiate the Second Component
The second component is \( 3x^{3} \). Use the power rule for derivatives: The derivative of \( cx^{n} \) is \( cnx^{n-1} \). Therefore, the derivative of \( 3x^{3} \) is \( 9x^{2} \).
04
Differentiate the Third Component
The third component is a constant, \( 12 \). The derivative of any constant is \( 0 \).
05
Combine the Derivatives
Combine the derivatives from the previous steps to find the derivative of the entire function: \( f'(x) = -x(625-x^{2})^{-1/2} + 9x^{2} + 0 \). Thus, the derivative simplifies to \( f'(x) = -\frac{x}{\sqrt{625-x^{2}}} + 9x^{2} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chain Rule
The chain rule is a fundamental technique in calculus for finding the derivative of composite functions. A composite function is essentially a function within another function, and the chain rule helps break down these layers to find the derivative.
- To use the chain rule, identify the outer and inner functions. In our exercise, \( \sqrt{625-x^{2}} \) can be rewritten as \( (625-x^{2})^{1/2} \), where \( u = 625-x^{2} \) is the inner function.
- The outer function in this setup is \( u^{1/2} \). The chain rule formula is \( \frac{d}{dx}[u^{n}] = nu^{n-1} \cdot u' \).
- First, differentiate the outer function: \( \frac{d}{dx}[u^{1/2}] = \frac{1}{2}u^{-1/2} \).
- Then, differentiate the inner function (\( u = 625-x^{2} \)): \( u' = -2x \).
- Combine these results: The derivative of the entire composite function is \( -x(625-x^{2})^{-1/2} \).
Power Rule
The power rule is one of the easiest and most frequently used rules for finding derivatives. It simplifies the process by providing a straightforward method for differentiating functions of the form \( cx^{n} \).
- If you have a function \( f(x) = cx^{n} \), the power rule states that its derivative is \( f'(x) = cnx^{n-1} \).
- For the exercise at hand, consider the component \( 3x^{3} \). According to the power rule, differentiate it as follows: \( 3 \cdot 3x^{3-1} \).
- This gives us the derivative \( 9x^{2} \).
- Notice how the power of \( x \) is reduced by one while the coefficient is multiplied by the original exponent.
Derivative of a Constant
When it comes to derivatives, constants have a special rule of their own: they simply vanish. This is because the derivative measures the rate of change, and a constant, by its nature, doesn't change.
- If you have a constant value like \( c \), its derivative is always \( 0 \).
- For example, in our function, we have the constant term \( 12 \). Its derivative is \( 0 \) because it doesn't change as \( x \) changes.
- This simplification often helps to streamline the differentiation process by eliminating any constant terms immediately.