In triangle XYZ, we know exactly which angle we mean when we say angle X, so in such a case, 1 letter will do. But in the next picture, there are four different angles at B, namely angles ABD, ABE, DBC and CBE, so if I say angle B, which one do I mean? Therefore, it's best to use 3 letters to name an angle if there's more than one angle at a common vertex. In the diagram above, it's easy to see what angle we mean when we say angle B. Sometimes, we use only 1 letter to name an angle, but that can be confusing when there's more than one angle at the same vertex. The angle above can be named either ABC or CBA - note that B, the vertex, is in the middle, between A and C. We generally name angles like the one in the diagram above with 3 letters and we always put the vertex letter between the other two just the way it appears in the picture. They rotate around a fixed point - (if they didn't, they'd fly off the bus) - through an angle large enough so that together, they wipe enough of the windshield for the driver to see clearly. Think about the windshield wipers on the school bus. Turning is also called rotating - so angles are the result of a rotation or turn. Once we've got the cover of our math book open, we TURN the page. Then we turned BA upwards to create the angle ABC. It's as if BA started out lying on top of BC, pinned down at B. The line segments AB and BC are the arms.īC is called the initial arm and AB is called the terminal arm. The point where they meet on the book's spine, is the vertex. With our book, the bottom edges of the cover and first page are the arms and The lines which meet to form the angle are called arms. The point at which the lines meet is called the vertex. When you open your math book part way as in the picture, the bottom edge of the cover forms an acute angle with the bottom edge of the first page.Īn angle is formed when 2 lines meet at a point.
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