Chapter 10: Problem 78
If a \(30^{\circ}-60^{\circ}-90^{\circ}\) triangle and an isosceles right triangle have the same perimeter, which will have the greater area? Why?
Short Answer
Expert verified
The 30°-60°-90° triangle has a greater area.
Step by step solution
01
Understand the Perimeters
Identify the properties of a 30°-60°-90° triangle and an isosceles right triangle. For a 30°-60°-90° triangle, the sides are in the ratio 1:√3:2, and for an isosceles right triangle, the sides are in the ratio 1:1:√2.
02
Define the Perimeters
Let the sides of the 30°-60°-90° triangle be a, a√3, and 2a. The perimeter is a + a√3 + 2a = a(3 + √3). Let the sides of the isosceles right triangle be b, b, and b√2. The perimeter is b + b + b√2 = b(2 + √2).
03
Equalize the Perimeters
Set the perimeters of both triangles equal to each other: a(3 + √3) = b(2 + √2). Simplify to find a in terms of b, or vice versa.
04
Calculate the Areas
For the 30°-60°-90° triangle, the area is (1/2)ab, with b = a√3. For the isosceles right triangle, the area is (1/2)b^2. Express the areas using the sides in terms of a single variable.
05
Simplify the Area Comparison
Use the relationship between a and b from step 3 to compare the areas of the two triangles.
06
Conclusion
Determine which triangle has the greater area based on the simplified expressions from step 5.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
30-60-90 Triangle
A 30°-60°-90° triangle is a special right triangle with unique properties. The angles are always 30 degrees, 60 degrees, and 90 degrees. This triangle has sides in a specific ratio: 1 : √3 : 2. This means:
- The shortest side (opposite the 30° angle) is 'a'.
- The side opposite the 60° angle is 'a√3'.
- The hypotenuse (opposite the 90° angle) is '2a'.
Isosceles Right Triangle
An isosceles right triangle is another special kind of triangle. It has a right angle (90 degrees) and two equal angles of 45 degrees each. The sides of an isosceles right triangle are in the ratio 1 : 1 : √2. This means:
- Each leg (the sides forming the right angle) is 'b'.
- The hypotenuse (the side opposite the right angle) is 'b√2'.
Perimeter
The perimeter of a triangle is the sum of its side lengths. For the 30°-60°-90° triangle with sides 'a', 'a√3', and '2a', the perimeter is:a + a√3 + 2a = a(3 + √3).
- For the isosceles right triangle with sides 'b', 'b', and 'b√2', the perimeter is:b + b + b√2 = b(2 + √2).When these perimeters are equal, we set up the equation:
- a(3 + √3) = b(2 + √2). From here, we solve for 'a' in terms of 'b' to understand their relationship better. This relationship allows us to compare different properties like area.
Area Calculation
The area of a triangle is given by (1/2) base × height.For the 30°-60°-90° triangle:Area = (1/2) * a * a√3 = (a^2√3)/2.For the isosceles right triangle:Area = (1/2) * b * b = (b^2)/2.To compare the areas, we use the relationship between 'a' and 'b' derived from the perimeter equality:a(3 + √3) = b(2 + √2).From this, we get 'a' in terms of 'b' or vice versa. Then: Places these expressions in the area formulas, simplifying and comparing, shows which has the larger area.