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A degree is a unit of measurement for angles and arcs. It is written as a small circle [°]. You can write 90° or 90 degrees. There are 360 degrees in a circle.
The denominator is the bottom number of a fraction. In the fraction 1/3, the denominator is 3. It indicates the number of parts needed to make a whole unit.

A diagonal is a line from one vertex (corner) of a quadrilateral to the opposite vertex.
The diameter is the length of a straight line through the center of a circle.
A dividend is a number to be divided. In the equation 12 ÷ 2 = 6, 12 is the dividend.