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Printable Cosine Law Worksheet | Grade 10–11 Math
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This cosine law worksheet helps Grade 10–11 students find unknown sides and angles in oblique triangles, decide between the sine law and cosine law, and apply both to real distance problems. Twenty-eight tasks move from direct substitution to Canadian-context applications, so students build accuracy and method choice together.
At a Glance
- Grade: 10–11 · Subject: Math
- Standard:
HSG-SRT.D.11— Use the sine law and cosine law to find unknown sides and angles- Skill Focus: Cosine law for sides and angles, choosing the right law
- Format: 3 pages · 28 problems · Answer key included · PDF
- Best For: Trigonometry practice and review
- Time: 35–45 minutes
What's Inside
The worksheet has four parts on 3 pages: finding a side, finding an angle, choosing between the sine law and cosine law, and applications. Every part opens with a worked example, and a 3-page answer key lists each solution. Students keep full calculator precision until the final step, then round sides and angles to the nearest tenth.
Skill Progression
- Guided practice: Parts A and B open with worked examples that show substitution step by step for sides and angles.
- Supported practice: Part C gives a decision rule (sine law for an angle and its opposite side, cosine law for SAS or SSS) and asks students to name the law before solving.
- Independent practice: Part D asks students to sketch, label, choose a law, and solve in Canadian-context settings such as a northern Ontario canoe route.
The sequence follows gradual release: I Do, We Do, You Do.
Standards Alignment
HSG-SRT.D.11 — Understand and apply the Law of Sines and the Law of Cosines to find unknown measurements in right and non-right triangles. This standard code can be copied directly into lesson plans, IEP goals, or district curriculum mapping tools.
How to Use It
Use it after direct instruction on the cosine law as guided practice, with students working Parts A and B in pairs. You can also assign Parts C and D as review before a unit test. While students work, watch Part C: students who start calculating before naming the law need more practice recognizing SAS, SSS, and angle-side pairs. Expect 35–45 minutes.
Who It's For
Built for Grade 10–11 math students learning to solve oblique triangles, including students reviewing trigonometry. Worked examples and the decision rule support learners who need scaffolds, while the sketch-and-solve applications stretch stronger students. Pair it with a sine law anchor chart or a direct instruction lesson on SAS and SSS triangles.
Standard HSG-SRT.D.11 asks students to apply the Law of Sines and Law of Cosines to find unknown measurements in non-right triangles. This Grade 10–11 cosine law worksheet puts that skill into 28 tasks across 3 pages: finding a side from two sides and the included angle, finding an angle from three sides, choosing between the sine law and cosine law, and solving four sketch-and-solve application problems set in Canadian parks and other outdoor settings. Each part opens with a worked example, and a 3-page answer key shows final values rounded to the nearest tenth. Fisher & Frey (2014) describe gradual release of responsibility, moving from modeled examples to independent work, as a reliable way to build durable procedural skill, and the part-by-part structure follows that sequence. Teachers can use the worksheet for practice, review, or formative checks on method selection.
