Trigonometry basics
Use the trigonometric ratios sin, cos, and tan in right-angled triangles to find unknown sides and angles, including setting up the correct ratio for a given problem
Teaching approaches
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1 approach
In a right triangle, sine compares opposite to hypotenuse, cosine compares adjacent to hypotenuse, and tangent compares opposite to adjacent: SOH CAH TOA. The ratio must match the known and unknown sides. Inverse sine, cosine, or tangent finds an angle when the side lengths are known.
Spend 15 minutes labeling a right triangle, choosing the correct ratio, and solving one side problem and one angle problem with a calculator in degree mode.
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Check understanding
- Identify which trigonometric ratio to use (SOH CAH TOA) based on the known and unknown sides
- Calculate an unknown side using sin, cos, or tan and a known angle
- Find an unknown angle using the inverse trigonometric function (e.g. tan⁻¹)
“If your child knows a ladder is 5 metres long and leans against a wall at 70° to the ground, can they use trigonometry to work out how high up the wall it reaches?”
Curriculum record
- Type
- Procedural
- Subject
- Mathematics
- Domain
- Geometry
- Age range
- Ages 13–15
Standards