M4.3.5 For the adult
Finding angles
A ramp rises 1 m while it goes 4 m along the ground. What angle does it make with the ground?
What this chapter teaches
When two sides are known and the angle is wanted, the learner picks sin, cos or tan from the sides, divides them, and presses the inverse key on the calculator. The learner also learns that a sine or cosine in a right angled triangle is between 0 and 1, and that sin⁻¹ means the inverse, not 1 ÷ sin.
Three questions to ask
There is no one right wording. Listen for the idea.
- How do you choose between sin⁻¹, cos⁻¹ and tan⁻¹ for a given triangle?
- Why can a sine never be above 1 in a right angled triangle?
- What does the inverse key do that the plain sin key does not?
After the chapter, the learner can
- Use inverse sin, cos or tan to find an angle
- Find the angle of a slope from its height and length
What they copy into their notebook
Two sides known, angle wanted. Pick sin, cos or tan. Divide the sides, then press the inverse key. Use degrees mode.