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 $180^{\circ}.$

Division : Division is the mathematical operation that divides objects equally into groups. More generally $x\div y$ is defined as the number that if multiplied by $y$ equals $x.$

Standard algorithm : By standard algorithm we refer to any one of the algorithms that are commonly taught at school to add, subtract, multiply or divide multi-digit numbers such as long division and partial products multiplication.

Decimal : A decimal is a number represented by digits in front and after a decimal point. In front of the decimal point the digits are the ones digit, tens digit, hundreds digit and so on. After the decimal point there are the tenths digit, hundredths digit, thousandths digit and so on. For example the decimal 1.3 can be written as $1\frac{3}{10}.$

Infinity : Infinity or $\infty$ represents a number that is bigger than all numbers in $\mathbb{R}.$

Irrational number : An irrational number is a real number that can not be written as a fraction. $\sqrt{2}$ and $\pi$ are examples of irrational numbers.

Period : A decimal is called periodic with period $a_1a_2,\ldots,a_n$ if the sequence $a_1a_2,\ldots,a_n$ keeps on repeating forever in the decimal. For example $\frac{1}{3}=0.3333\ldots=0.\overline{3}$ has a period equal to 3. A function $f$ is called periodic with period $a$ if $f(x+a)=f(x)$ for all $x.$

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.

Square root : The square root of $x$ denoted by $\sqrt{x}$ is the positive number such that $(\sqrt{x})^2=\sqrt{x}\cdot \sqrt{x}=x.$ For example $\sqrt{9}=3.$

Square root of 2 : The square root of 2 also written as $\sqrt{2}$ is the positive number such that $(\sqrt{2})^2=\sqrt{2}\cdot \sqrt{2}=2.$ $\sqrt{2}$ is an irrational number and rounded to the nearest hundredths it is equal to 1.41.