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10th grade Area of a triangle without a height: sine formula and Heron's formula worksheet

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Area of a triangle without a height: sine formula and Heron's formula

Grade 10 Math Worksheet - Building Confidence

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Circle the best answer, or write your answer on the line.

  1. Pia's tent side is triangle FGH with FG = 13 ft and angle G = 77°. The height FD meets GH at a right angle. To the nearest tenth, how long is FD, in feet?

  2. Ren's garden bed is triangle FGH with FG = 10 m and angle G = 33°. The height FD meets GH at a right angle. To the nearest tenth, how long is FD, in meters?

  3. Tala's paper flag is triangle FGH with FG = 14 cm and angle G = 58°. The height FD meets GH at a right angle. To the nearest tenth, how long is FD, in centimeters?

  4. Zee's sandwich half is triangle FGH with FG = 7 cm, GH = 12 cm, angle G = 80° and angle H = 33°. Which expression gives its area?

    • ½ × 7 × 12
    • ½ × 7 × 12 × sin 80°
    • ½ × 7 × 12 × sin 33°
    • 7 × 12 × sin 80°
  5. Ari's pennant is triangle FGH with FG = 9 in, GH = 13 in, angle G = 70° and angle H = 40°. Which expression gives its area?

    • ½ × 9 × 13 × sin 40°
    • ½ × 9 × 13 × sin 70°
    • 9 × 13 × sin 70°
    • ½ × 9 × 13
  6. Bo's garden bed is triangle FGH with FG = 10 ft, GH = 7 ft, angle G = 65° and angle H = 73°. Which expression gives its area?

    • 10 × 7 × sin 65°
    • ½ × 10 × 7 × sin 65°
    • ½ × 10 × 7
    • ½ × 10 × 7 × sin 73°
  7. Esme's park lawn is triangle FGH with FG = 12 m, GH = 9 m, angle G = 35° and angle H = 97°. Which expression gives its area?

    • ½ × 12 × 9 × sin 35°
    • ½ × 12 × 9
    • ½ × 12 × 9 × sin 97°
    • 12 × 9 × sin 35°
  8. Jun's sail is triangle FGH with FG = 9 cm and GH = 14 cm. Its height FD is 6.9 cm. To the nearest tenth, what is its area, in square centimeters?

  9. Kira's pizza slice is triangle FGH with FG = 11 in and GH = 16 in. Its height FD is 6.8 in. To the nearest tenth, what is its area, in square inches?

  10. Luz's tent door is triangle FGH with FG = 7 ft and GH = 12 ft. Its height FD is 6.2 ft. To the nearest tenth, what is its area, in square feet?

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10th grade Area of a triangle without a height: sine formula and Heron's formula worksheet – printable
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About this worksheet

Area of a triangle without a height: sine formula and Heron's formula. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can find the height of a triangle from a side and an angle with sine.
  • I can find a triangle's area as ½ × side × side × sine of the angle between them.
  • I can use Heron's formula when I know all three sides.

Standard: G-SRT.D.9 (+); Heron's formula has no CCSS code (G-MG.A.1 related)

Words to know

height: The segment from a corner to the opposite side, meeting it square.

included angle: The angle where the two known sides meet.

sine (sin): In a right triangle: opposite side ÷ hypotenuse.

degrees mode: The calculator setting that reads angles in degrees, shown as DEG.

s (semiperimeter): Half the distance around the triangle.

Common mistakes

Left out the ½ in a triangle's area. A triangle is half of a parallelogram with the same sides. Cut a paper parallelogram along a diagonal together.

Used cosine where sine belongs. The height is opposite the angle, so it uses sine. Label opposite, adjacent and hypotenuse together.

Used a calculator set to radians, so every sine came out wrong. Check that the calculator shows DEG before using sine.

Questions parents ask

What is the most common mistake with area of a triangle without a height: sine formula and heron's formula?

Left out the ½ in a triangle's area. A triangle is half of a parallelogram with the same sides. Cut a paper parallelogram along a diagonal together.

Are these 10th grade math worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

More geometry

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