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In Exercises 48 and 49 , assume that the graph of the exponential function \(f(x)=k \cdot a^{x}\) passes through the two points. Find the values of \(a\) and \(k .\) $$(1,1.5),(-1,6)$$

Short Answer

Expert verified
The values for \(a\) and \(k\) are 3 and 0.5 respectively.

Step by step solution

01

Formulate Equations from Points

The function is given by \(f(x) = k \cdot a^{x}\). We know that the graph of the function passes through the points (1,1.5) and (-1,6). We can create two equations from these two points.\nFrom the first point, substitute \(x = 1\) and \(f(x) = 1.5\) into the function equation to get \(1.5 = k \cdot a\).\nFrom the second point, substitute \(x = -1\) and \(f(x) = 6\) into the function equation to get \(6 = k \cdot a^{-1} = \frac{k}{a}\).
02

Solve for a

We have a system of two equations, \(1.5 = k \cdot a\) and \(6 = \frac{k}{a}\), and two unknowns, \(a\) and \(k\). \nMultiply the two equations to eliminate \(k\). The result is \(1.5 \cdot 6 = a \cdot \frac{k}{a} \cdot k \cdot a\), which simplifies to \(9 = a^{2}\). Take the square root on both sides to find \(a = \pm3\). Because \(a > 0\) in an exponential function, we can discard the negative value. So, \(a = 3\).
03

Solve for k

Now, substitute \(a = 3\) back into the first equation to find \(k\). This gives \(1.5 = k \cdot 3 \Rightarrow k = \frac{1.5}{3} = 0.5\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Solving Systems of Equations
When solving problems involving multiple equations with multiple unknowns, we enter the realm of systems of equations. A system of equations is a collection of two or more equations with a same set of unknowns. In our exercise, we have the equations from the points of the exponential function:
  • \(1.5 = k \cdot a\)
  • \(6 = \frac{k}{a}\)
To solve these, we aim to find values for \(a\) and \(k\) that satisfy both conditions.
Here's a quick strategy:
  • First, express one variable in terms of the other, if possible.
  • Second, substitute expressions to reduce the number of unknowns.
  • Finally, solve for the unknowns by substituting back into the original equations.

In this example, by multiplying the equations, we eliminate one variable, allowing us to solve for the other. The crucial step is simplifying to find \(9 = a^2\), from which we determine \( a = 3 \) by considering the properties of exponential functions that require \(a > 0\).
Function Graphs
Function graphs are a core visualization tool in mathematics. Each function has its own distinct graph that tells a story. These graphs help us understand equations' behaviors, identify patterns, and see relationships between variables.
An exponential function, like \( f(x) = k \cdot a^x \), grows or decays rapidly.
  • If the base \(a\) is greater than 1, the function represents exponential growth.
  • If \(a\) is between 0 and 1, the function depicts exponential decay.

In our case with \(a = 3\), this indicates strong exponential growth. The graph of our function passes through the points (1,1.5) and (-1,6). Observing such a graph shows:
  • The rate and direction of change.
  • Positions of specific points along the curve.
  • The steepness or slope at various parts of the curve. More steep means faster growth.
By analyzing these points and their equations, we visualize how the exponential function behaves across different sections of its graph.
Exponential Growth
Exponential growth is a process that increases quantity over time, characterized by the mathematical function \(f(x) = k \cdot a^x\), where \(a > 1\). The importance of exponential growth lies in its real-world applications, such as population dynamics, financial investments, and scientific data analysis.
In our function, with determined values \(a = 3\) and \(k = 0.5\), each increase in \(x\) results in a threefold increase in \(f(x)\). This depicts characteristic exponential growth, where small changes in \(x\) result in significant changes in \(f(x)\).
Key aspects of exponential growth include:
  • Increases at a constant rate per unit interval.
  • Doubling time or tripling time—indicating the time it takes for a quantity to double or triple.
  • Rapid change can quickly lead to enormous values.
In conclusion, understanding exponential functions and their graphs are foundational in various scientific and financial fields, helping to predict growth patterns and make strategic decisions.

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Most popular questions from this chapter

Let \(y_{1}=x^{2}\) and \(y_{2}=2^{x}\) . (a) Graph \(y_{1}\) and \(y_{2}\) in \([-5,5]\) by \([-2,10] .\) How many times do you think the two graphs cross? (b) Compare the corresponding changes in \(y_{1}\) and \(y_{2}\) as \(x\) changes from 1 to \(2,2\) to \(3,\) and so on. How large must \(x\) be for the changes in \(y_{2}\) to overtake the changes in \(y_{1} ?\) (c) Solve for \(x : x^{2}=2^{x}\) . \(\quad\) (d) Solve for \(x : x^{2}<2^{x}\)

Multiple Choice Which of the following gives the domain of \(f(x)=\frac{x}{\sqrt{9-x^{2}}}\) \(\begin{array}{ll}{\text { (A) } x \neq \pm 3} & {\text { (B) }(-3,3)} \\\ {(\mathrm{D})(-\infty,-3) \cup(3, \infty)} & {(\mathrm{E})(3, \infty)}\end{array}\)

Exploration Let \(y=a \sin x+b \cos x\) Use the symbolic manipulator of a computer algebra system (CAS) to help you with the following: (a) Express y as a sinusoid for the following pairs of values: a=2, b=1 ; \quad a=1, b=2 ; \quad a=5, b=2 ; \quad a=2, b=5 a=3, b=4 (b) Conjecture another formula for \(y\) for any pair of positive integers. Try other values if necessary. (c) Check your conjecture with a CAS. (d) Use the following formulas for the sine or cosine of a sum or difference of two angles to confirm your conjecture. \(\begin{aligned} \sin \alpha \cos \beta & \pm \cos \alpha \sin \beta=\sin (\alpha \pm \beta) \\ \cos \alpha \cos \beta \pm \sin \alpha \sin \beta &=\cos (\alpha \mp \beta) \end{aligned}\)

Cholera Bacteria Suppose that a colony of bacteria starts with 1 bacterium and doubles in number every half hour. How many bacteria will the colony contain at the end of 24 \(\mathrm{h}\) ?

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