Count : To count means to find out the number of objects by adding one for every object.

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 $180^{\circ}.$

Distributive property : The distributive property is defined by $a(x+y)=ax+ay$ for all $a,x,y.$ The distributive property is implicitly used whenever one multiplies out brackets or uses standard algorithms for multiplication or division.

Follow from : A second equation or inequality follows from an initial equation or inequality if all solutions of the initial equation are also solutions from the second equation or inequality. It does not necessarily have to be the case that all solutions of the second equation or inequality have to by solutions of the first inequality. For example $x^2=1$ follows from $x=1$, but $x^2=1$ is not equivalent to $x=1$ as -1 is a solution of $x^2=1$ but not a solution of $x=1.$

Multiplication : Multiplication is the mathematical operation that is a shorthand for adding the same amount several times. For example $3\cdot 4=4+4+4=12.$

Negative : A number is negative if it is $\lt 0.$

Number : A number $x$ is a mathematical symbol representing a quantity.

Counterclockwise : Counterclockwise specifies a direction of a rotation in the opposite direction of the direction in which the hands of a clock are moving.

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

Right angle : A right angle is an angle equal to $90^{\circ}.$

Right triangle : A right triangle is a triangle that has a right angle. The sides that form the right angle are called legs, the third side is called hypotenuse. The area of a right triangle is half the product of the lengths of the two legs. The Pythagorean theorem is an important theorem for right triangles that allows to calculate the third side of a right triangle given the other two.

Rotation : A rotation is a transformation that turns a shape around. A rotation turns shapes into congruent shapes.

Straight angle : A straight angle is an angle equal to $180^{\circ}.$