Here is a short vid covering special triangles, but it's a refresher not a lesson from scratch or an introductory lesson...so it kind of starts in the middle and assumes the student has some familiarity with the subject.
The camera work is, as usual not awesome, but you get the info. You can also start to see how it all goes together, with square numbers and expressing numbers using radicals. We also again have the five basic concepts clearly on display we are just counting we never count past nine only count stuff that is same, concept of same, using rectangles to make it easy to count in this case squares, and of course the concept of ONE: No Fun Get Back To One, in both making one side of the triagle one but also by dividing out the sin cos or tan of an angle to get one x or y which is the length of a side or hypotenuse. This is where we begin to develop critical thinking skills and reasoning the computation is relatively easy...as expressed in the teenager terms, "OMG that's all there is to it?"
You can build triangles using the blocks as sides and learn a lot about the relationships that way. Here is a screencast on Pythagoras' Theorem:
Note that one you understand this, the special triangles make all kinds of sense and you are just playing with making one of the sides ONE, then you can use algebra to make generalizations about them. This math stuff is easy...as long as you can see the pictures and the pictures make sense. The last building block is of course square numbers because the worksheet wanted the sides expressed as radicals:
Here is a little more on that:
Yet more on radicals:
And how to introduce these concepts to little kids:
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