Chapter 4: Problem 83
Suppose that \(f(2)=-4, g(2)=1, f^{\prime}(2)=0\), and \(g^{\prime}(2)=-2\). Let \(y=f(x) /(2 g(x)) ;\) find \(\frac{d y}{d x}\) when \(x=2\).
Short Answer
Expert verified
The derivative \( \frac{d y}{d x} \) at \( x=2 \) is \(-4\).
Step by step solution
01
Identify the function values
We begin by recognizing the function values given for calculation: \( f(2) = -4 \), \( g(2) = 1 \), \( f'(2) = 0 \), and \( g'(2) = -2 \). These will be used to find the derivative of \( y \) using the quotient rule.
02
Apply the Quotient Rule
The quotient rule states that if \( y = \frac{u}{v} \), then its derivative \( y' \) is given by \( \frac{d y}{d x} = \frac{u'v - uv'}{v^2} \). For \( y = \frac{f(x)}{2g(x)} \), let \( u = f(x) \) and \( v = 2g(x) \), then \( v' = 2g'(x) \).
03
Differentiate the Numerator and Denominator
Calculate \( u' = f'(x) \) and \( v' = 2g'(x) \). Given \( f'(2) = 0 \) and \( g'(2) = -2 \), thus \( u'(2) = 0 \) and \( v'(2) = 2(-2) = -4 \).
04
Substitute into the Quotient Rule Formula
Substitute the values: \( u = f(2) = -4 \), \( u'(2) = 0 \), \( v = 2g(2) = 2\times 1 = 2 \), and \( v'(2) = -4 \) into the quotient rule: \[\frac{d y}{d x} = \frac{0 \cdot 2 - (-4) \cdot (-4)}{2^2} = \frac{0 - 16}{4} = \frac{-16}{4}\]
05
Simplify the Result
Simplify the expression \( \frac{-16}{4} \) to get \( -4 \). Thus, at \( x = 2 \), \( \frac{d y}{d x} = -4 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quotient Rule
The quotient rule is a fundamental concept in calculus used to find the derivative of a division of two functions. It is particularly useful when you have a function expressed as the ratio \( \frac{u}{v} \). Here, \( u \) and \( v \) are functions of \( x \). The quotient rule states that the derivative of this ratio is:
In our exercise, \( u \) corresponds to \( f(x) \) and \( v \) corresponds to \( 2g(x) \). When using the quotient rule, calculate the derivatives of both \( u \) and \( v \) to substitute them into the formula.
- \( \frac{d}{dx} \left( \frac{u}{v} \right) = \frac{u'v - uv'}{v^2} \)
In our exercise, \( u \) corresponds to \( f(x) \) and \( v \) corresponds to \( 2g(x) \). When using the quotient rule, calculate the derivatives of both \( u \) and \( v \) to substitute them into the formula.
Derivative Calculation
Derivative calculation is a process in calculus used to find the rate at which a function is changing at any given point. It's a crucial method for understanding the behavior of functions. In simple terms, differentiation gives you the slope of the tangent line to the curve at any point.
- In the exercise, we're interested in the derivative of \( y = \frac{f(x)}{2g(x)} \) at \( x=2 \).
- Using known values: \( f'(2) = 0 \) and \( g'(2) = -2 \), derivatives of the numerator and denominator were calculated as \( u'(2) = f'(2) = 0 \) and \( v'(2) = 2g'(2) = -4 \).
Function Evaluation
Function evaluation is determining the output of a function for a particular input. This step is straightforward but crucial in applying rules like the quotient rule.
- For example, in our exercise, we evaluate functions \( f(x) \) and \( g(x) \) at \( x = 2 \).
- Given values were \( f(2) = -4 \) and \( g(2) = 1 \). These values are necessary to substitute into the derivative formula.
Differentiation
Differentiation is a fundamental concept in calculus that deals with finding the rate at which a quantity changes. It is represented mathematically as the process of finding a derivative.
This process is instrumental in understanding how functions behave. In the exercise, differentiation was applied to solve for \( \frac{d y}{d x} \) of \( y=\frac{f(x)}{2g(x)} \).
This process is instrumental in understanding how functions behave. In the exercise, differentiation was applied to solve for \( \frac{d y}{d x} \) of \( y=\frac{f(x)}{2g(x)} \).
- We use rules like the quotient rule to differentiate more complex expressions, breaking them down into simpler tasks.
- Given \( f'(2) = 0 \) and \( v'(2) = -4 \), we substitute these into the quotient rule formula.
- The final derivative calculation simplifies to \( \frac{d y}{d x} = -4 \) when \( x = 2 \).