Introducing Trig Ratios

Today I had the chance to co-teach a lesson introducing trigonometry with a 2P math class. The students started out up at the boards learning how to label right angle triangle sides and angles with lowercase and uppercase letters, and the words hypotenuse, opposite and adjacent sides.

Next they worked through some examples of calculating sides with the pythagorean theorem.

The next challenge was on graph paper: they needed to draw a 90 degree angle on their page. Then draw a right triangle with one angle that is 30 degrees. We estimated the other acute angle, then measured it to be sure. Just to prove to them that angles in a triangle add to 180 we did this demonstration (but I forgot to get pictures).

photo source

Next we used rulers and measured the side lengths of the triangle, as precisely as possible.

We put the values in a table to compare. And I magically was able to judge the accuracy of their triangle skills and accuracy of measuring.

We talked through what was special about the ones that were done “perfectly”. Students identified that the short side was half of the long side for those cases.

From there we explored the primary trig ratios and how to remember them with the acronym SOH CAH TOA.