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Area of Triangle Using Trigonometry

HSG-SRT.D.9
Answer Keys Here

Aligned To Common Core Standard:

High School Geometry - HSG-SRT.D.9

How to Determine the Area of a Triangle Using Trigonometry - We all know the general formula for calculating the area of a triangle. It is expressed as: A= 1/2 b x h | In the above formula, 'b' is defined as the base or length of a side, where 'h' is defined as the height draw to the side. Reading from the above formula, we say that the area of the triangle is half the length of one side times the height drawn with it. However, there is another way to measure the area of a triangle. Trigonometry is not only used to find different angles and sides of a right-angled triangle; we use trigonometry to calculate the area of a triangle. Using the above right-angled triangle, we can say, sin C = h/b. Multiplying the above equation by b, we get: b sinC = h. The height of the triangle can now be written as b sinC. Replacing this new value of height in the general formula for calculating the area of a triangle. A= 1/2 ab sin C. Where the letters 'a' and 'b' express any two sides of the triangle, and C represents the included angle. With this derived formula, we aren't required to find the height of the triangle. If you know the two sides and their included angle, you can substitute these values in this formula to find the area of the triangle. What an awesome selection of worksheets and lessons to allow students to learn how to use trig. to solve problems that involve finding the areas of triangles.

Printable Worksheets And Lessons




Homework Sheets

I still remember the first day I saw this skill. It was so powerful!

  • Homework 1 - Express the area rounded to three decimal places.
  • Homework 2 - In an isosceles triangle, the two equal sides each measure 5 meters, and they include an angle of 85°. Find the area of the isosceles triangle, to the nearest square meter.
  • Homework 3 - In Triangle PQR, PQ = 8, PR = 4, and m




Practice Worksheets

The practice sheets give you a good balance of questions to work with.

  • Practice 1 - In Δ UVW, UV = 7, UW = 18, and m < U = 34°. Find the area of Δ UVW, to the nearest tenth of a square unit.
  • Practice 2 - Why would you positon a triangle to the right, when it could go left?
  • Practice 3 - In a rhombus, each side is 24, and one angle is 175°. Find the area of the rhombus, to the nearest square unit.



Math Skill Quizzes

The last quiz seems to be the most difficult for kids.

  • Quiz 1 - In triangle PQR, PQ = 30 meters and PR = 21 meters. If the area of the triangle is 210 sq. meters, find the measure of < P to the nearest degree.
  • Quiz 2 - Using Heron's formula, find the area of the triangle, to the nearest tenth.
  • Quiz 3 - In an isosceles triangle, the two equal sides each measure 25 meters, and they include an angle of 55°. Find the area of the isosceles triangle, to the nearest sq. meter.