Question
LeSSOn20 3.7 The chain rule: Probien (1 point) Find the derivative of \( y \) using the appropriate combination of rules. \( y=(9 x+4)^{\frac{1}{2}} \) \( y^{\prime}=\square \) Preview My Answers Submit Answers
Ask by Huang Harper. in the United States
Mar 09,2025
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Tutor-Verified Answer
Answer
\( y' = \frac{9}{2} (9x+4)^{-\frac{1}{2}} \)
Solution
1. Identify the outer function and the inner function:
- Outer function: \( u^{\frac{1}{2}} \) where \( u = 9x+4 \)
- Inner function: \( u = 9x + 4 \)
2. Differentiate the outer function with respect to \( u \):
\[
\frac{d}{du}\left(u^{\frac{1}{2}}\right) = \frac{1}{2} u^{-\frac{1}{2}}
\]
3. Differentiate the inner function \( u = 9x + 4 \) with respect to \( x \):
\[
\frac{du}{dx} = 9
\]
4. Apply the chain rule by multiplying the derivatives:
\[
y' = \frac{1}{2} u^{-\frac{1}{2}} \cdot 9 = \frac{9}{2} (9x+4)^{-\frac{1}{2}}
\]
5. The derivative is:
\[
y' = \frac{9}{2} (9x+4)^{-\frac{1}{2}}
\]
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Bonus Knowledge
To find the derivative of \( y = (9x + 4)^{\frac{1}{2}} \), we can apply the chain rule. The outer function is the square root, and the inner function is \( 9x + 4 \). The derivative of the outer function, \( u^{\frac{1}{2}} \), is \( \frac{1}{2} u^{-\frac{1}{2}} \), and for the inner function \( u = 9x + 4 \), its derivative is \( 9 \). So, using the chain rule: \[ y' = \frac{1}{2}(9x + 4)^{-\frac{1}{2}} \cdot 9 = \frac{9}{2(9x + 4)^{\frac{1}{2}}} \] Thus, the derivative \( y' = \frac{9}{2(9x + 4)^{\frac{1}{2}}} \).