Properties of Right Triangles

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SAT Math › Properties of Right Triangles

Questions 1 - 10
1

A right triangle has legs of lengths $10$ and $24$. What is the perimeter of the triangle?

$26$

$58$

$34$

$60$

Explanation

To find the perimeter, we need all three sides: the two legs (10 and 24) plus the hypotenuse. Using the Pythagorean theorem: 10² + 24² = 100 + 576 = 676, so the hypotenuse = √676 = 26. The perimeter is 10 + 24 + 26 = 60. A common mistake is forgetting to find the hypotenuse first, or calculating area instead of perimeter. This uses the 5-12-13 Pythagorean triple scaled by 2.

2

A square has side length $10$. The diagonal of the square forms the hypotenuse of a right triangle whose legs are the sides of the square. What is the length of the diagonal?​

$100$

$52$

$102$

$20$

Explanation

The question asks for the length of the diagonal in a square with side length 10, where the diagonal forms the hypotenuse of a right triangle with the sides as legs. Apply the Pythagorean theorem: diagonal d = √(10² + 10²) = √(100 + 100). Compute 100 + 100 = 200, so d = √200 = √(100 × 2) = 10√2. A key error is treating it as a 45-45-90 triangle but forgetting to multiply by √2, resulting in just 10. Some might double the side incorrectly to get 20. Remember that in squares, the diagonal is always side × √2, which simplifies calculations without full recomputation.

3

In the diagram, triangle $ABC$ is a right triangle with the right angle at $C$. The legs are $AC=9$ cm and $BC=12$ cm. What is the length of the hypotenuse $AB$?​

$5$ cm

$21$ cm

$225$ cm

$15$ cm

Explanation

The question asks for the length of the hypotenuse AB in right triangle ABC with a right angle at C and legs AC = 9 cm and BC = 12 cm. Use the Pythagorean theorem, which states that in a right triangle, the square of the hypotenuse equals the sum of the squares of the legs. Apply the formula: AB = √(AC² + BC²) = √(9² + 12²). Calculate 9² = 81 and 12² = 144, so 81 + 144 = 225, and √225 = 15 cm. A common error is adding the legs instead of their squares, which would give an incorrect 21 cm. Another mistake might be squaring the sum of the legs, leading to √(21)² = 21, but that's not the theorem. When facing Pythagorean problems, verify if it's a multiple of a known triple like 3-4-5, here scaled by 3 to 9-12-15.

4

A 13-foot ladder leans against a vertical wall. The base of the ladder is 5 feet from the wall on level ground. How high up the wall does the ladder reach, in feet?​

$18$

$12$

$8$

$144$

Explanation

The question asks how high up the wall a 13-foot ladder reaches when its base is 5 feet from the wall, forming a right triangle. Use the Pythagorean theorem, where the ladder is the hypotenuse, the base is one leg, and the height is the other leg. Solve for height h: h = √(13² - 5²) = √(169 - 25). Calculate 169 - 25 = 144, and √144 = 12 feet. Students might err by subtracting squares incorrectly or forgetting the square root, yielding 144 instead of 12. Another common mistake is adding the squares, giving √(169 + 25) = √194, which is irrelevant here. A useful strategy is to recognize 5-12-13 as a Pythagorean triple for quick verification.

5

A right triangle has hypotenuse length $14$ and one leg length $7$. What is the length of the other leg?​

$98$

$73$

$21$

$147$

Explanation

The question asks for the length of the other leg in a right triangle with hypotenuse 14 and one leg 7. Apply the Pythagorean theorem rearranged to find the missing leg: leg2 = √(hypotenuse² - leg1²) = √(14² - 7²). Calculate 14² = 196 and 7² = 49, so 196 - 49 = 147, and √147 = √(49 × 3) = 7√3. Ensure subtraction is in the correct order, as reversing would give a negative under the square root. A frequent error is adding instead of subtracting, leading to √(196 + 49) = √245, which is incorrect. Some might divide the hypotenuse by 2, but that's not applicable here. When verifying, check if the sides satisfy a² + b² = c² after solving.

6

A ramp rises to a platform that is 3 meters high. The ramp is 5 meters long. Assuming the ground is level, how far from the base of the platform is the bottom of the ramp, in meters?​

$8$

$16$

$4$

$2$

Explanation

The question asks for the horizontal distance from the base of a 3-meter-high platform to the bottom of a 5-meter-long ramp, assuming level ground. Model this as a right triangle with hypotenuse 5 (ramp), one leg 3 (height), and the other leg as the base b. Use Pythagorean theorem: b = √(5² - 3²) = √(25 - 9). Calculate 25 - 9 = 16, so √16 = 4 meters. A common error is using addition instead, yielding √(25 + 9) = √34, which is incorrect. Another mistake might be treating the height as the hypotenuse, leading to invalid negatives. Recognize 3-4-5 as a Pythagorean triple for efficient solving without recalculation.

7

A 20-foot ladder leans against a vertical wall. The bottom of the ladder is 12 feet from the wall on level ground. How high up the wall does the ladder reach, in feet?​

$32$

$ 2144$

$8$

$16$

Explanation

This problem asks how high the ladder reaches on the wall, which is one leg of a right triangle. The ladder forms the hypotenuse (20 feet), and the distance from wall to ladder base is the other leg (12 feet). Using the Pythagorean theorem: 12² + h² = 20², so 144 + h² = 400, giving h² = 256 and h = 16 feet. A common mistake is subtracting the base distance from the ladder length (20 - 12 = 8) instead of using the Pythagorean theorem. Visualizing the right triangle formed by the wall, ground, and ladder helps identify which measurements correspond to which sides.

8

On the coordinate plane, what is the distance between the points $(-2,3)$ and $(4,-5)$?​

$\sqrt{28}$

$\sqrt{52}$

$10$

$\sqrt{100}$

Explanation

This problem asks for the distance between two points using the distance formula, which is derived from the Pythagorean theorem. The distance formula is d = √[(x₂-x₁)² + (y₂-y₁)²]. Substituting: d = √[(4-(-2))² + (-5-3)²] = √[6² + (-8)²] = √[36 + 64] = √100 = 10. Common errors include sign mistakes when subtracting coordinates or forgetting to square the differences. The distance √100 simplifies to 10, not left as √100.

9

A rectangle has length $10$ and width $6$. What is the length of its diagonal?​

$\sqrt{64}$

$8$

$16$

$\sqrt{136}$

Explanation

This question asks for the diagonal of a rectangle, which forms the hypotenuse of a right triangle with the length and width as legs. Using the Pythagorean theorem: diagonal² = 10² + 6² = 100 + 36 = 136, so diagonal = √136. Students often make arithmetic errors (like 10 + 6 = 16) or try to simplify √136 incorrectly (√136 ≠ √64 = 8). Leave the answer as √136 unless asked to approximate, as this is the exact value.

10

In a $30^\circ$-$60^\circ$-$90^\circ$ right triangle, the hypotenuse has length $18$. What is the length of the longer leg?​

$6\sqrt{3}$

$9\sqrt{3}$

$18\sqrt{3}$

$9$

Explanation

This problem asks for the longer leg in a 30°-60°-90° triangle with hypotenuse 18. In a 30°-60°-90° triangle, the sides are in ratio 1 : √3 : 2, where the hypotenuse is 2x, the shorter leg is x, and the longer leg is x√3. Since hypotenuse = 18 = 2x, we get x = 9, so the longer leg = 9√3. Common errors include using 9 as the answer (the shorter leg) or multiplying incorrectly to get 18√3. Memorizing the 30°-60°-90° ratio pattern helps solve these problems quickly.

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