In these worksheets, students will learn to find the value of a missing angle of a triangle.

How Do You Find Missing Angles by Using Trigonometry? Geometry is a fun branch of mathematics but sometimes it can be a bit troublesome. Many students find it difficult when it comes to finding missing angles in triangles. We all know that there are three angles in triangles and their sum is equal to 180°. When two angles are given, we can find the third one by subtracting the sum of the given angles from 180°. Things get complicated when you have one or no given angle and only the sides are given. This is where trigonometry comes in. We can solve for missing angles using trigonometric functions. Staring with right-triangles, here we know one angle which is 90°. Now you have to find the other angles. To get started with it, you need to know that the side opposite to the 90° angle is hypotenuse, then there is the base and perpendicular. We have three basic trigonometric functions and these are; sin⁡α = Opposite/Hypotenuse, cos⁡α = Adjacent/Hypoenuse, tan⁡α = (Opposite )/Adjacent. You can use these to find the missing angles. Now, if you are dealing with non-right-angle triangles you will have to use Sine and Cosine rules. Sine Rule is used when three sides and two angles are given. The Sine Rule is; a/sin⁡A = b/sin⁡B = c/sin⁡C. Cosine rule is used when three sides are given. The Cosine Rule is; a2 =b2 +c2 -2ab cos⁡A. b2 =a2 +c2 -2ac cos⁡B. c2 =a2 +b2 -2ac cos⁡C.

In these worksheets, students will use trigonometry to find the missing angle value of a triangle. Diagrams are included on each worksheet for students to reference. They will read the information specified about each triangle and fill in blank with the value of the missing angle. Extra paper may be required in order for students to do their calculations. This set of worksheets contains lessons, step-by-step solutions to sample problems, both simple and more complex problems, a review, and a quiz. It also includes ample worksheets for students to practice independently. Most worksheets contain between eight and ten problems. When finished with this set of worksheets, students will be able to use trigonometry to find the missing angle value. These worksheets explain how to use trigonometry to find the value of a missing angle of a triangle. Sample problems are solved and practice problems are provided.

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Finding Missing Angle Trigonometrically Worksheets

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This worksheet explains how to use trigonometry to find the value of a missing angle. A sample problem is solved, and two practice problems are provided.

Find the Missing Angle Trigonometrically Worksheet

Feel free to use an trigonometry based theorem of your choice to find the value of a missing angle. Ten problems are provided.


See if your knowledge of triangle geometry can help you find the measures of the missing angles.

Review and Practice

The concept of how to use trigonometry for these types of problems is reviewed. A sample problem is solved. Six practice problems are provided.


Students will demonstrate their proficiency with these types of problems. Ten problems are provided.

Skills Check

Students will use their experience with trigonometry to find the value of a missing angle. Three problems are provided, and space is included for students to copy the correct answer when given.