Understanding Inverse Variation

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Questions and Answers

In an inverse variation, if one variable increases, what happens to the other variable?

  • It increases proportionally.
  • It stays constant.
  • It increases exponentially.
  • It decreases. (correct)

Which equation represents an inverse variation, where $x$ and $y$ are variables and $k$ is a non-zero constant?

  • $x - y = k$
  • $x/y = k$
  • $xy = k$ (correct)
  • $x + y = k$

If the time it takes to travel a certain distance varies inversely with speed, what happens to the travel time if the speed is doubled?

  • It remains the same.
  • It quadruples.
  • It is halved. (correct)
  • It doubles.

If $y$ varies inversely as $x$, and $y = 6$ when $x = 4$, find the value of $y$ when $x = 8$.

<p>3 (A)</p> Signup and view all the answers

If the time it takes for a group to complete a task varies inversely with the number of people working on it, what does this imply?

<p>The total work done is constant, regardless of the number of people. (D)</p> Signup and view all the answers

If $a$ varies inversely as $b^2$, and $a = 3$ when $b = 2$, find $a$ when $b = 4$.

<p>0.75 (B)</p> Signup and view all the answers

The electrical current in a circuit with constant voltage varies inversely with the resistance. If the current is 2 amps when the resistance is 10 ohms, what is the current when the resistance is 5 ohms?

<p>4 amps (A)</p> Signup and view all the answers

Assume the number of seats in a room stay constant. How does the space allotted to each seat change with the number of people sitting in the seats?

<p>It varies inversely. (C)</p> Signup and view all the answers

The volume of a gas at constant temperature varies inversely with the pressure exerted on it (Boyle's Law). If the volume of a gas is 10 liters at a pressure of 2 atmospheres, what is the volume when the pressure is increased to 5 atmospheres?

<p>4 liters (B)</p> Signup and view all the answers

In an inverse variation relationship, which statement is always true about the variables $x$ and $y$?

<p>As $x$ approaches infinity, $y$ approaches zero. (D)</p> Signup and view all the answers

The per capita share of expenses varies inversely with the number of people sharing the expenses. If four people share expenses and each pays $50, how much will each person pay if ten people share the same expenses?

<p>$20 (D)</p> Signup and view all the answers

The number of teeth on two connected gears varies inversely with the number of revolutions per minute (RPM) they make. If a large gear has 60 teeth and makes 30 RPM, how many RPM will a smaller gear with 20 teeth make?

<p>90 RPM (D)</p> Signup and view all the answers

Flashcards

Inverse Variation

A relationship where the product of two variables is constant.

Constant of Variation (k)

The constant value in an inverse variation equation.

Inverse Variation Equation

Expressed as xy = k, where k is a non-zero constant.

Relationship in Inverse Variation

As one variable increases, the other decreases proportionally.

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Bike Ride Example

Time taken to cover a distance varies inversely with speed.

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Formula for biking

rate × time = distance

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Cooling Water Example

Cooling speed varies inversely with the temperature difference.

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Breaking a Board Example

Force needed varies inversely with the board's length.

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Stringed Instruments

Finger placement is determined by the inverse variation between string length and vibration frequency.

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Study Notes

  • Inverse variation describes relationships where one quantity increases as the other decreases.

Real-Life Example: Biking Speed and Time

  • The time it takes to cover a specific distance varies inversely with speed.
  • The equation rate × time = distance (or time = distance / rate) represents this scenario.
  • For a 20-mile bike ride, averaging 20 mph results in a 1-hour ride. Reduced speed to 10mph doubles the time to 2 hours.

Definition of Inverse Variation

  • An inverse variation is a relationship where the product of two variables equals a constant.
  • Mathematically expressed as xy = k, where k is a non-zero constant.

Equations, Tables, and Graphs

  • The inverse variation equation can be rewritten as y = k/x.
  • When x is large, y is small, and when x is small, y is large.
  • Inverse variation graphs are curves, not straight lines as seen in linear relationships.

Tables Examples

  • k=1
    • x = 1/4, y = 4
    • x = 1/2, y = 2
    • x = 1, y = 1
    • x = 2, y = 1/2
    • x = 10, y = 1/10
  • k=100
    • x = 1, y = 100
    • x = 2, y = 50
    • x = 10, y = 10
    • x = 50, y = 2
    • x = 100, y = 1

Other Real-Life Examples

  • How quickly a glass of cold water cools down on a warm day varies inversely with the temperature.
  • The force required to break a board varies inversely with its length.
  • String length and vibration frequency have an inverse variance.

Lesson Summary

  • Inverse variation occurs when the product of two variables is constant (xy = k, where k ≠ 0).
  • When one variable increases, the other decreases proportionally.
  • Examples include stringed instruments, warming water, and bike rides.

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