Solve with changing area using related rates

Brian McLogan
6 Nov 201603:49
EducationalLearning
32 Likes 10 Comments

TLDRThe video script discusses the rate of change of the area of a square with respect to time. It introduces a scenario where the side length of the square, denoted as 'x', varies with time and is growing at a rate of two feet per minute. The area 'a' is defined as the square of the side length, x^2. The script then explains the process of differentiating the area with respect to time to find the rate of change. At the specific moment when the side length is three feet, the rate of increase of the area is calculated to be 12 square feet per minute, providing a clear understanding of how quickly the area of the square is expanding.

Takeaways
  • πŸ“ The problem involves a square whose side length (x) varies with time, representing the area as a function of x (A = x^2).
  • πŸ”„ The rate of change of the area (dA/dt) is being investigated, which requires differentiation with respect to time.
  • 🎯 At the specific time when the side length is 3 feet, the rate of change of the area (dA/dt) needs to be calculated.
  • πŸš€ The side length (x) is growing at a constant rate of 2 feet per minute, represented as dx/dt = 2 ft/min.
  • πŸ“ˆ The derivative of the area function with respect to time is found to be dA/dt = 2x * dx/dt.
  • πŸ“Œ At the time when x = 3 feet, the derivative calculation becomes dA/dt = 2 * 3 * 2 = 12 ft^2/min.
  • πŸ”’ The result of 12 ft^2/min indicates the area is increasing at a rate of 12 square feet per minute when the side length is 3 feet.
  • 🌟 The units of the rate of change (ft^2/min) correctly reflect the concept of area increasing over time.
  • πŸ‘“ The process highlights the importance of understanding both the constant values and the rates of change in a problem involving time-varying dimensions.
  • 🧩 This problem is an example of how mathematical concepts such as differentiation can be applied to real-world scenarios, like the growth of an object's area over time.
  • πŸ“š The script provides a step-by-step approach to solving problems that involve both a formula for an area and a rate of change with respect to time.
Q & A
  • What is the formula used to calculate the area of a square?

    -The formula to calculate the area of a square is A = x^2, where A represents the area and x represents the length of the side of the square.

  • How does the side length of a square vary with time?

    -The side length of a square, denoted as x, is assumed to vary with time. This means that x is a function of time and can be represented as x(t), where t is time.

  • What does the rate of change of the side length represent?

    -The rate of change of the side length, denoted as dx/dt, represents the speed at which the side length of the square is increasing or decreasing with respect to time.

  • What is the relationship between the rate of change of the area and the rate of change of the side length?

    -The rate of change of the area (dA/dt) is related to the rate of change of the side length (dx/dt) through the derivative of the area formula with respect to time. This relationship is given by the equation dA/dt = 2x(dx/dt).

  • What is the specific rate at which the side length is growing when x is 3 feet?

    -When the side length x is 3 feet, it is growing at a rate of 2 feet per minute, which is represented as dx/dt = 2 ft/min.

  • How can we find the rate of increase of the area when the side length is 3 feet?

    -To find the rate of increase of the area when the side length is 3 feet, we can substitute x = 3 ft and dx/dt = 2 ft/min into the derivative of the area formula. This gives us dA/dt = 2*3*2 = 12 ft^2/min.

  • What units are used to express the rate of change of the area with respect to time?

    -The units used to express the rate of change of the area with respect to time are square feet per minute (ft^2/min), since the area is in square feet and the time is in minutes.

  • What is the role of differentiation in this problem?

    -Differentiation is used to find the rate at which the area of the square is changing with respect to time. It helps us calculate the derivative of the area formula with respect to time, which gives us the rate of change.

  • What is the significance of the constant 2 in the derivative formula dA/dt = 2x(dx/dt)?

    -The constant 2 in the derivative formula dA/dt = 2x(dx/dt) comes from the derivative of the side length squared. It represents the factor by which the side length changes affect the rate of change of the area.

  • How does the rate of change of the area depend on the current side length?

    -The rate of change of the area depends on the current side length because as the side length increases or decreases, the area changes at a rate proportional to the square of the side length. This is reflected in the derivative formula where the current side length x is multiplied by the rate of change of the side length (dx/dt).

  • What is the final expression for the rate of change of the area in this problem?

    -The final expression for the rate of change of the area in this problem is dA/dt = 2x(dx/dt). When x = 3 ft and dx/dt = 2 ft/min, the expression becomes dA/dt = 2*3*2 = 12 ft^2/min.

Outlines
00:00
πŸ“ Calculating the Rate of Change of a Square's Area

This paragraph discusses the mathematical problem of finding the rate at which the area of a square is increasing. The square's side length, denoted by 'x', is given to be 3 feet and is growing at a rate of 2 feet per minute. The speaker first establishes the formula for the area of a square (A = x^2) and then differentiates this formula with respect to time (t) to find the rate of change of the area (dA/dt). By substituting x = 3 feet and the rate of change of x (dx/dt = 2 feet/min), the speaker calculates that the area is increasing at a rate of 12 square feet per minute at the given time.

Mindmap
Keywords
πŸ’‘Area
The term 'area' refers to the amount of space inside a two-dimensional shape, such as a square. In the context of the video, it is the primary focus as the calculation of the area of a square (side length squared) is central to understanding how the area changes over time. The script mentions 'let a be the area of a square' to establish the mathematical relationship that a = x^2, where 'x' represents the side length of the square.
πŸ’‘Square
A 'square' is a geometric shape with four equal sides and four right angles. It is a specific type of rectangle. In the video, the square is the subject of the mathematical problem, where the area of the square is of interest. The properties of a square are used to derive the formula for the area, which is side length squared (x^2).
πŸ’‘Side Length
The 'side length' is the measure of one side of a square. In the video, the side length is denoted by 'x' and is described as varying with time, which implies that the size of the square is changing. The rate of change of the side length is given as two feet per minute, which is crucial in calculating how quickly the area of the square is increasing.
πŸ’‘Rate of Change
The 'rate of change' is a mathematical term that describes how quickly a quantity changes with respect to another quantity. In the video, it is used to determine how fast the area of the square is increasing as the side length changes. The rate of change is symbolized by 'dx/dt' for the side length and 'da/dt' for the area.
πŸ’‘Differentiate
To 'differentiate' is to find the derivative of a function, which gives the rate of change of the function with respect to one of its variables. In the context of the video, differentiation is used to find the rate at which the area of the square is increasing (da/dt) based on the original area formula (a = x^2).
πŸ’‘Time
In the context of the video, 'time' is the independent variable with respect to which changes in the side length and area of the square are measured. The problem involves calculating the rate of change of the area at a specific time when the side length is three feet and growing at a rate of two feet per minute.
πŸ’‘Constant
A 'constant' is a value that does not change within the context of a particular problem or mathematical expression. In the video, the constant is related to the initial side length of the square, which is given as three feet when calculating the rate of change of the area.
πŸ’‘Growth Rate
The 'growth rate' refers to the speed at which a quantity increases. In the video, the growth rate is specifically the rate at which the side length of the square is increasing, which is given as two feet per minute. This growth rate is essential for calculating the rate of change of the area of the square.
πŸ’‘Per Minute
The phrase 'per minute' indicates the unit of time over which the rate of change is measured. In the video, it is used to express the growth rate of the side length of the square, which is two feet per minute. This unit is crucial for understanding the time frame relevant to the calculations.
πŸ’‘Feet
The term 'feet' refers to a unit of length in the imperial system, equivalent to 12 inches or approximately 0.3048 meters. In the video, 'feet' is the unit used to measure both the side length of the square and the growth rate of the side length.
πŸ’‘Feet Squared
The term 'feet squared' refers to a unit of area in the imperial system, used to express the size of a two-dimensional space. In the video, the area of the square is measured in feet squared, and the rate of change of the area is calculated in terms of 'feet squared per minute'.
Highlights

The problem involves a square whose side length varies with time, represented as x.

The side length of the square, x, is given as 3 feet at a certain time.

The rate of change of the side length (dx/dt) is 2 feet per minute.

The area of the square is represented by the equation A = x^2.

To find the rate of change of the area with respect to time, the formula is differentiated with respect to time.

The derivative of the area with respect to time is represented as dA/dt = 2x(dx/dt).

At the side length of 3 feet, the rate of change of the area (dA/dt) is to be determined.

The area is increasing and the problem seeks the rate of this increase.

The mathematical model used is based on the principles of calculus to determine rates of change.

The final calculated rate of change of the area is 12 square feet per minute when the side length is 3 feet and growing at 2 feet per minute.

The units of the rate of change of the area are in square feet per minute, which is appropriate for the area of a square.

The problem demonstrates the application of calculus in understanding the dynamics of geometric shapes.

The process involves identifying the constant (side length at a given time) and the rate (growth rate of the side length).

The problem-solving approach requires differentiating the area formula to find the rate of change.

The problem illustrates the relationship between the side length of a square and its area.

The solution process is systematic, emphasizing understanding the variables and their rates of change.

The problem is relevant for practical applications such as physics and engineering where the dimensions of objects change over time.

The transcript provides a step-by-step explanation of how to solve the problem, which is helpful for educational purposes.

Transcripts
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