The multiplicative identity shows us that any time you multiply something by the number 1, the result would be what you started with.
Ex: 1(m) or 1 x m.
The reason for thusbis that when you are multiplying you are representing groups of something, so 1 group of anything or m, would just be that anything or m in this case!
Let's rename angle BAC to w. Now, we have four angles: w, x, y, and z. We know that w + y + z has to equal 180 degrees, because a triangle's three angels always adds up to 180 degrees. We also know that w + x equals 180 degrees, because they are on the same line. These two phrases are equal:
