Circle : A circle is a two-dimensional shape. The boundary of a circle is a set of points that has the same distance (the radius) from the center of the circle.

Corner : A corner of a shape is a point in the shape such that this point does not lie on the line segment between any two other points in the shape. Every triangle has 3 corners and every quadrilateral has 4 corners.

Hexagon : A hexagon is a polygon with six corners. The sum of the angles in a hexagon is $720^{\circ}.$

Shape : A shape is a set of points in space.

Square : A square is a quadrilateral with four right angles and four equal length sides. A square is a special case of a rectangle and a special case of a rhombus.

Triangle : A triangle is a polygon with three corners and three sides. You can calculate the area of a triangle by multiplying half the length of the base by the height on that base. The sum of the interior angles in a triangle is always $180^{\circ}.$

Addition : Addition is the mathematical operation that describes increasing a number by an amount equal to a second number. The mathematical symbol for addition is the plus sign $+.$ The term addition is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.

Multiple : A multiple of a number $x$ is any of the numbers $1x,2x,3x,4x,\ldots.$ For example the multiples of 7 include 7, 14, 21 and 70.

Composite function : The composite function $h=f\circ g$ is defined by $h(x)=f(g(x)).$ For example for the functions $f(x)=x^2$ and $g(x)=x+1$ the composite function $h=f\circ g$ is the function $h(x)=(x+1)^2.$ The composite function of two continuous functions is continuous. The composite function of two differentiable functions is differentiable and the derivative can be calculated using the chain rule.

Function : A function is a mapping in which every element in one set is mapped to exactly one element of a second set. Most often the mapping is described using a rule. For example the function $f(x)=x+1$ maps 2 to 3 and -1 to 0.

Graph : The graph of a function is the set of points $\{(x,f(x))\}$ that can be blotted in a coordinate system.

Point : A point is an element in a space. Shapes are made of sets of points.

Reflection : A reflection is a transformation that mirrors a shape at a line. Reflections turn shapes into congruent shapes.

X-axis : The horizontal axis in a two-dimensional coordinate system.

Y-axis : The vertical axis in a two-dimensional coordinate system.