Area of a triangle without a height: sine formula and Heron's formula
Grade 10 Math Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.
Milo's sail is triangle FGH with FG = 12 cm and angle G = 40°. The height FD meets GH at a right angle. To the nearest tenth, how long is FD, in centimeters?
Noah's pizza slice is triangle FGH with FG = 9 in and angle G = 20°. The height FD meets GH at a right angle. To the nearest tenth, how long is FD, in inches?
Sketch, not to scale: triangle FGH with GH along the bottom. FD is dashed from F straight down to GH, with a right-angle mark at D. FG = 9 in, angle G = 20°. Sketch, not to scale: triangle FGH with GH along the bottom. FD is dashed from F straight down to GH, with a right-angle mark at D. FG = 9 in, angle G = 20°. G H F D 9 in 20° Not to scale 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?
Sketch, not to scale: triangle FGH with GH along the bottom. FD is dashed from F straight down to GH, with a right-angle mark at D. FG = 10 m, angle G = 33°. Sketch, not to scale: triangle FGH with GH along the bottom. FD is dashed from F straight down to GH, with a right-angle mark at D. FG = 10 m, angle G = 33°. G H F D 10 m 33° Not to scale 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?
Sketch, not to scale: triangle FGH with GH along the bottom. FD is dashed from F straight down to GH, with a right-angle mark at D. FG = 14 cm, angle G = 58°. Sketch, not to scale: triangle FGH with GH along the bottom. FD is dashed from F straight down to GH, with a right-angle mark at D. FG = 14 cm, angle G = 58°. G H F D 14 cm 58° Not to scale 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?
Sketch, not to scale: triangle FGH with FG = 7 cm, GH = 12 cm, angle G = 80°, angle H = 33° and angle F = 67° (to the nearest degree). Sketch, not to scale: triangle FGH with FG = 7 cm, GH = 12 cm, angle G = 80°, angle H = 33° and angle F = 67° (to the nearest degree). F G H 7 cm 12 cm 80° 33° 67° Not to scale - ½ × 7 × 12 × sin 33°
- ½ × 7 × 12
- 7 × 12 × sin 80°
- ½ × 7 × 12 × sin 80°
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?
Sketch, not to scale: triangle FGH with FG = 9 in, GH = 13 in, angle G = 70°, angle H = 40° and angle F = 70° (to the nearest degree). Sketch, not to scale: triangle FGH with FG = 9 in, GH = 13 in, angle G = 70°, angle H = 40° and angle F = 70° (to the nearest degree). F G H 9 in 13 in 70° 40° 70° Not to scale - ½ × 9 × 13 × sin 40°
- ½ × 9 × 13
- ½ × 9 × 13 × sin 70°
- 9 × 13 × sin 70°
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?
Sketch, not to scale: triangle FGH with FG = 10 ft, GH = 7 ft, angle G = 65°, angle H = 73° and angle F = 42° (to the nearest degree). Sketch, not to scale: triangle FGH with FG = 10 ft, GH = 7 ft, angle G = 65°, angle H = 73° and angle F = 42° (to the nearest degree). F G H 10 ft 7 ft 65° 73° 42° Not to scale - ½ × 10 × 7
- 10 × 7 × sin 65°
- ½ × 10 × 7 × sin 65°
- ½ × 10 × 7 × sin 73°
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?
Sketch, not to scale: triangle FGH with FG = 12 m, GH = 9 m, angle G = 35°, angle H = 97° and angle F = 48° (to the nearest degree). Sketch, not to scale: triangle FGH with FG = 12 m, GH = 9 m, angle G = 35°, angle H = 97° and angle F = 48° (to the nearest degree). F G H 12 m 9 m 35° 97° 48° Not to scale - 12 × 9 × sin 35°
- ½ × 12 × 9 × sin 35°
- ½ × 12 × 9 × sin 97°
- ½ × 12 × 9
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?
Sketch, not to scale: triangle FGH with base GH = 14 cm. FD = 6.9 cm is dashed from F to GH at a right angle. FG = 9 cm and angle G = 50°. Sketch, not to scale: triangle FGH with base GH = 14 cm. FD = 6.9 cm is dashed from F to GH at a right angle. FG = 9 cm and angle G = 50°. 6.9 cm G H F D GH = 14 cm 9 cm 50° Not to scale Milo's picnic lawn is triangle FGH with FG = 13 m and GH = 20 m. Its height FD is 9 m. To the nearest tenth, what is its area, in square meters?
Sketch, not to scale: triangle FGH with base GH = 20 m. FD = 9 m is dashed from F to GH at a right angle. FG = 13 m and angle G = 44°. Sketch, not to scale: triangle FGH with base GH = 20 m. FD = 9 m is dashed from F to GH at a right angle. FG = 13 m and angle G = 44°. 9 m G H F D GH = 20 m 13 m 44° Not to scale