ABCs of Geometry “The hardest part of math last week was adding all the decimals on the restaurant menu.” –Student 6

A is for Acute Angle Acute angles are less than 90 degrees. An equilateral triangle has three acute angles. How many acute angles does an obtuse triangle have?

B is for Base The base is the bottom of a three-dimensional figure in geometry. What if the top is parallel to the bottom? Can you think of an example?

C is for Congruent If angles or figures are congruent, they are the same shape and size. If there are no numbers on a picture, how can we tell if the sides and angles are congruent?

D is for Degree A degree ( °) is a unit of measure of an angle. The sum of all three angles in a triangle always equals 180 degrees. How many degrees are in a circle?

E is for Equilateral Triangle Equilateral triangles have three equal sides and angles. Each of the angles is always 60 degrees. If the angles are always the same size, can the side lengths vary?

F is for Face A face is a flat surface of a three-dimensional figure. Prisms can have many faces. How can you usually tell how many faces a prism has without counting? This is one of eight faces. This is one of five faces.

G is for Geometry Geometry is the study of two-dimensional and three- dimensional figures. It uses relationships between points, lines, angles and surfaces. Does anyone know what “geometry” literally means?

H is for Hypotenuse The hypotenuse is the side that is opposite the right angle in a right triangle. The other two sides of a right triangle are called opposite and adjacent. Can a triangle have more than one right angle?

I is for Isosceles Triangle An isosceles triangle has two equal sides. By default, there are also two equal angles. Are isosceles triangles always acute (like the pictures)?

J is for Journal Writing is a way for students to communicate their understanding of geometry. Writing helps connect prior knowledge to polygons, angles and lines. How do journals help both teachers and students?

K is for Kite A kite is a quadrilateral with two pairs of adjacent sides that are congruent. –Note the hash marks What must the diagonals of a kite always be? –Hint: look at the pink box in the picture

L is for Line of Symmetry A line of symmetry divides a geometric figure into two congruent portions. A dotted line usually shows a line of symmetry. Does the letter “L” have a line of symmetry?

M is for Midpoint The midpoint is the point on a line segment that divides it into two congruent pieces. A line segment can only have one midpoint. Why does a line not have a midpoint?

N is for Nonagon A Nonagon is a nine-sided polygon. The Figure shown is a regular nonagon (all sides equal length). Are the angles all equal?

O is for Obtuse Angle Obtuse angles are larger than 90 °. Obtuse triangles can be scalene or isosceles. How many obtuse angles can an obtuse triangle have?

P is for Parallelogram A parallelogram is a quadrilateral. It has 2 pairs of opposite sides that are parallel. What can we say about the diagonals?

Q is for Quadrilateral A quadrilateral is a four- sided polygon. Polygons are closed figures with line segments for sides. What is an example of a quadrilateral?

R is for Rectangle A rectangle has four 90 ° angles. The opposite sides are congruent. Can a rectangle also be a square?

S is for Supplementary Angles Supplementary angles are two angles that add up to 180 degrees. <A + <B =180 What is the supplementary angle for an angle of 42 ° ?

T is for Trapezoid A trapezoid is a quadrilateral. It has one set of parallel sides. Are all three of these figures trapezoids?

U is for Undecagon (also called “Hendecagon”) An Undecagon is a polygon that had eleven sides. The figure is a regular polygon because all the sides are of equal length. Are the angles equal?

V is for Vertex A vertex is where two lines/rays intersect to form an angle. It is also the corners on a polygon. What do the sides and vertices have in common? (in the figure with the red arrow)

W is for Word Problem A word problem is a way to ask math questions. The information in the problem is presented in word form rather than mathematical notation. What are word problems also called?

X is for X-axis The X-axis is a horizontal line on a Cartesian graph. It runs through the origin (0,0). How could we write an equation for the x-axis in y= form?

Y is for Y-axis The Y-axis is a vertical line on a Cartesian graph. It also runs through the origin (0,0). How could we write an equation for the y-axis?

Z is for Zero Angle A Zero angle is an angle that measures 0 degrees. Depending on the context, the same angle could also be considered 360 °. Is a zero angle (0°, not 360°) an obtuse, acute, or right angle?. 0°

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