Chapter 12: Problem 37
The area of an ellipse with axes of length \(2 a\) and \(2 b\) is \(A=\pi a b\). Approximate the percent change in the area when \(a\) increases by \(2 \%\) and \(b\) increases by \(1.5 \%\)
Short Answer
Expert verified
Answer: The percent change in the area of the ellipse is approximately 3.53%.
Step by step solution
01
Write down the area formula for an ellipse
The area formula for an ellipse is given by \(A = \pi a b\)
02
Calculate the new values for a and b
When a increases by 2%, we get \(a_{new} = a + 0.02a = 1.02a\)
When b increases by 1.5%, we get \(b_{new} = b + 0.015b = 1.015b\)
03
Find the new area
Now, let's calculate the new area using the updated values of a and b: \(A_{new} = \pi (1.02a)(1.015b)\)
04
Apply the percent change formula
The percent change formula is given by: \(\% \, Change = \frac{A_{new} - A}{A} \times 100\)
Substitute the values for \(A_{new}\) and \(A\) in the formula:
\(\% \, Change = \frac{\pi (1.02a)(1.015b) - \pi a b}{\pi a b} \times 100\)
05
Simplify the expression
Simplify the expression by factoring out \(\pi a b\):
\(\% \, Change = \frac{(1.02)(1.015) - 1}{1} \times 100\)
Calculate the value:
\(\% \, Change = (1.0353 - 1) \times 100 = 0.0353 \times 100\)
06
Step 6:Write down the final answer
The percent change in the area of the ellipse is approximately:
\(\% \, Change \approx 3.53 \%\)
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Ellipses
An ellipse is a fascinating geometric shape, often looked at as an elongated circle. It has two axes, namely the major axis and the minor axis. Imagine stretching a circle into an oval shape; that's your ellipse. The two axes have distinct names and uses:
- The **major axis** is the longest diameter, stretching across the widest part of the ellipse.
- The **minor axis** runs perpendicular to the major axis, spanning the shortest part across the ellipse.
Percent Change
Percent change is a way to express the amount of change over a particular period or due to a specific modification in terms of a percentage. It's a practical tool for comparing old and new values, commonly used in economics, statistics, and many real-world tasks.To calculate percent change, you'll use the formula:\[\%\, Change = \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \times 100\]In our ellipse context, this formula is applied to find the percentage change in the ellipse's area after changes in its axes.**Steps to Calculate:**
- Determine the original and new values you are comparing.
- Subtract the original value from the new value.
- Divide this by the original value to find the change as a fraction of the original.
- Multiply by 100 to convert the fraction into a percentage.
Area Calculation
Calculating area is a key part of understanding geometry and shapes. The area tells us how much two-dimensional space a shape covers. Whether calculating for rectangles, circles, or any special shapes like ellipses, it's essential to have the correct formula.**For Ellipses:**
- The area formula: \(A = \pi a b\) is specific to ellipses and is very distinct from other shapes like circles \(A = \pi r^2\) or rectangles \(A = \text{length} \times \text{width}\).
- This formula uses two parameters: the semi-major axis \(a\) and the semi-minor axis \(b\).
- Measure the lengths of axes correctly.
- Understand how changes in these lengths affect overall area.