Special Right Triangles
45-45-90 and 30-60-90 triangles
Special Right Triangles
45-45-90 Triangle
An isosceles right triangle with angles 45ยฐ, 45ยฐ, and 90ยฐ.
Side Ratios:
Where:
- = length of each leg
- = length of hypotenuse
Key Pattern: If legs = 1, then hypotenuse =
Example: If each leg is 5, hypotenuse =
30-60-90 Triangle
A right triangle with angles 30ยฐ, 60ยฐ, and 90ยฐ.
Side Ratios:
Where:
- = length of side opposite 30ยฐ (shortest side)
- = length of side opposite 60ยฐ
- = length of hypotenuse (opposite 90ยฐ)
Key Pattern: If short leg = 1, then long leg = , hypotenuse = 2
Example: If short leg is 6, long leg = , hypotenuse = 12
Why These Are Useful
- Appear frequently in geometry problems
- Can solve without Pythagorean Theorem
- Used in trigonometry
- Found in regular polygons and circles
Remember
45-45-90: legs equal, hypotenuse = leg ร
30-60-90: hypotenuse = 2 ร short leg, long leg = short leg ร
๐ Practice Problems
1Problem 1easy
โ Question:
In a 45-45-90 triangle, one leg measures 6. Find the length of the other leg and the hypotenuse.
๐ก Show Solution
Step 1: Recall 45-45-90 triangle properties: This is an isosceles right triangle If each leg = x, then hypotenuse = xโ2
Step 2: Identify the given information: One leg = 6
Step 3: Find the other leg: In a 45-45-90 triangle, both legs are equal Other leg = 6
Step 4: Find the hypotenuse: Hypotenuse = leg ร โ2 Hypotenuse = 6โ2
Step 5: Verify using Pythagorean Theorem: 6ยฒ + 6ยฒ = (6โ2)ยฒ 36 + 36 = 36 ร 2 72 = 72 โ
Answer: Other leg = 6, Hypotenuse = 6โ2
2Problem 2easy
โ Question:
In a 45-45-90 triangle, each leg has length 8. Find the hypotenuse.
๐ก Show Solution
In a 45-45-90 triangle, the hypotenuse = leg ร
Answer: (or approximately 11.31)
3Problem 3easy
โ Question:
In a 30-60-90 triangle, the shorter leg measures 5. Find the longer leg and the hypotenuse.
๐ก Show Solution
Step 1: Recall 30-60-90 triangle ratios: If shorter leg (opposite 30ยฐ) = x Then longer leg (opposite 60ยฐ) = xโ3 And hypotenuse = 2x
Step 2: Identify given information: Shorter leg = 5, so x = 5
Step 3: Find the longer leg: Longer leg = xโ3 = 5โ3
Step 4: Find the hypotenuse: Hypotenuse = 2x = 2(5) = 10
Step 5: Verify using Pythagorean Theorem: 5ยฒ + (5โ3)ยฒ = 10ยฒ 25 + 25(3) = 100 25 + 75 = 100 100 = 100 โ
Answer: Longer leg = 5โ3, Hypotenuse = 10
4Problem 4medium
โ Question:
In a 30-60-90 triangle, the hypotenuse is 20. Find both legs.
๐ก Show Solution
In a 30-60-90 triangle, sides are in ratio
Hypotenuse = :
Short leg (opposite 30ยฐ):
Long leg (opposite 60ยฐ):
Answer: Short leg = , Long leg =
5Problem 5medium
โ Question:
In a 30-60-90 triangle, the hypotenuse is 20. Find both legs.
๐ก Show Solution
Step 1: Recall the ratio: Shorter leg : Longer leg : Hypotenuse = x : xโ3 : 2x
Step 2: Use the hypotenuse to find x: Hypotenuse = 2x 20 = 2x x = 10
Step 3: Find the shorter leg: Shorter leg = x = 10
Step 4: Find the longer leg: Longer leg = xโ3 = 10โ3
Step 5: Verify: 10ยฒ + (10โ3)ยฒ = 20ยฒ 100 + 100(3) = 400 100 + 300 = 400 400 = 400 โ
Answer: Shorter leg = 10, Longer leg = 10โ3
6Problem 6medium
โ Question:
In a 45-45-90 triangle, the hypotenuse is 8โ2. Find the length of each leg.
๐ก Show Solution
Step 1: Recall the relationship: In a 45-45-90 triangle: If leg = x, then hypotenuse = xโ2
Step 2: Set up the equation: xโ2 = 8โ2
Step 3: Solve for x: x = 8โ2 / โ2 x = 8
Step 4: Both legs equal x: Each leg = 8
Step 5: Verify: 8ยฒ + 8ยฒ = (8โ2)ยฒ 64 + 64 = 64 ร 2 128 = 128 โ
Answer: Each leg = 8
7Problem 7hard
โ Question:
A 45-45-90 triangle has a hypotenuse of . Find the area of the triangle.
๐ก Show Solution
Step 1: Find the leg length
In 45-45-90 triangle: hypotenuse = leg ร
Step 2: Find area (both legs are equal)
Answer: Area = square units
8Problem 8hard
โ Question:
A square has a diagonal of length 10. Find the side length of the square and its perimeter.
๐ก Show Solution
Step 1: Recognize the special triangle: A square's diagonal divides it into two 45-45-90 triangles
Step 2: Set up the relationship: In a 45-45-90 triangle: If leg = s (side of square), then hypotenuse = sโ2 The diagonal is the hypotenuse
Step 3: Use the given diagonal: sโ2 = 10
Step 4: Solve for s: s = 10/โ2 s = 10/โ2 ร โ2/โ2 (rationalize) s = 10โ2/2 s = 5โ2
Step 5: Find the perimeter: Perimeter = 4s = 4(5โ2) = 20โ2
Step 6: Verify the diagonal: Using Pythagorean theorem: sยฒ + sยฒ = diagonalยฒ (5โ2)ยฒ + (5โ2)ยฒ = 10ยฒ 25(2) + 25(2) = 100 50 + 50 = 100 โ
Answer: Side length = 5โ2, Perimeter = 20โ2
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