When working with shapes in math class, students learn a new vocabulary. Among the terms they use are "length" and "width." To correctly solve geometry problems, students must correctly identify them. Using the basic shapes of rectangles and triangles, students can learn how to apply these terms to their mathematics classes.

Identify length and width with "horizontal" and "vertical." For rectangles in particular, the length is the horizontal side, while the width is the vertical side. This can be confusing, as the length is not necessarily the longest side, as one might expect.

Understand the implications of length and width for rectangles. The distinction between length and width has few real consequences for rectangles, as finding a rectangle's area involves multiplying them (making order irrelevant) and finding its perimeter involves adding all four sides together (where order is also irrelevant).

Apply this knowledge to triangles. Triangles have a specialized vocabulary: the length, or the bottom horizontal segment, is known as the base; the width is known as the height, measured from the uppermost point of the triangle to the base. This is because the length and width of a triangle varies as you progress through the shape, so using the terms "base" and "height" to describe these aspects of a triangle prevents confusion.
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