Chapter 27: Problem 9
Find the derivatives of the given functions. $$y=4 x^{3}-3 \csc \sqrt{2 x+3}$$
Short Answer
Expert verified
The derivative is \( y' = 12x^{2} + 3 \cdot \csc(\sqrt{2x+3}) \cdot \cot(\sqrt{2x+3}) \cdot (2x+3)^{-1/2} \).
Step by step solution
01
Analyze the Function
The function given is a combination of a polynomial and trigonometric expression: \( y = 4x^{3} - 3 \csc(\sqrt{2x+3}) \). To find the derivative, we need to apply basic differentiation rules, including the power rule and chain rule.
02
Apply the Power Rule
For the term \( 4x^{3} \), use the power rule: if \( f(x) = ax^n \), then \( f'(x) = anx^{n-1} \). Therefore, the derivative of \( 4x^{3} \) is \( 12x^{2} \).
03
Differentiate the Cosecant Term Using Chain Rule
For the term \(-3 \csc(\sqrt{2x+3})\), differentiate \(-\csc(u)\) using the chain rule. First, remember that the derivative of \( \csc(u) \) is \(-\csc(u)\cot(u)\). Let \( u = \sqrt{2x+3} \).
04
Find the Derivative of Inner Function
Find the derivative of \( u = \sqrt{2x+3} \). Rewriting \( u \) as \( (2x+3)^{1/2} \), its derivative is \( u' = \frac{1}{2} (2x+3)^{-1/2} \cdot 2 = (2x+3)^{-1/2} \).
05
Combine Derivatives Using Product Rule and Chain Rule
The derivative of \(-3\csc(\sqrt{2x+3})\) is \( 3 \cdot \csc(\sqrt{2x+3})\cdot \cot(\sqrt{2x+3})\cdot (2x+3)^{-1/2} \). This result is derived by applying the chain rule to the outside function \( -\csc \) and the inside function \( \sqrt{2x+3} \).
06
Final Combination of Derivatives
Combine the derivatives from steps 2 and 5 to get the final derivative: \[ y' = 12x^{2} + 3 \cdot \csc(\sqrt{2x+3}) \cdot \cot(\sqrt{2x+3}) \cdot (2x+3)^{-1/2} \].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Power Rule
The power rule is a cornerstone concept in calculus, especially when dealing with polynomial functions. It is a straightforward differentiation technique that simplifies the process of finding derivatives of power functions. The power rule states:
- If you have a function in the form of \( f(x) = ax^n \), where \( a \) is a constant, and \( n \) is a real number, the derivative \( f'(x) \) is obtained by multiplying the exponent by the coefficient and then subtracting one from the exponent. So the rule is \( f'(x) = anx^{n-1} \).
- Multiply the coefficient (4) by the exponent (3): \( 4 \times 3 = 12 \)
- Subtract 1 from the exponent (3): \( 3 - 1 = 2 \)
- The derivative is \( 12x^{2} \).
Chain Rule
The chain rule is an essential technique for finding derivatives of composite functions. A composite function is a function within another function, like \( g(f(x)) \). The chain rule helps us differentiate such functions by focusing on the outer and the inner functions separately.
- First, differentiate the outer function, keeping the inner function unchanged.
- Next, multiply the result by the derivative of the inner function.
- The derivative of \( u = \sqrt{2x+3} \) can be found by rewriting it as \( (2x+3)^{1/2} \).
- Differentiating \( (2x+3)^{1/2} \), we get \((2x+3)^{-1/2} \cdot 1 = (2x+3)^{-1/2} \).
- Multiplying these results gives us the derivative for the term \(-3 \csc(\sqrt{2x+3}) \).
Trigonometric Derivatives
Trigonometric derivatives allow us to find the rates of change for trigonometric functions like sine, cosine, and cosecant. When differentiating functions involving these trigonometric terms, having a good grasp of their derivatives is vital.
- The derivative of \( \sin(x) \) is \( \cos(x) \).
- For \( \cos(x) \), it is \(-\sin(x) \).
- Specifically, for the cosecant function, \( \csc(x) \), the derivative is \(-\csc(x) \cot(x) \).
- Calculate these derivatives using their known differentiation rules.
- Combine the results appropriately; for example, multiplying by any constants involved.