4 - Geometry

Here are few notions of geometry you should know...

Straight lines, semi-straight lines, and segments

 The straight line The segment The semi-straight line A straight line is a line with no beginning and no end, and therefore infinitely long. A segment is a line with two boundaries (or vertices). A semi-straight line is a line which has a boundary (or vetex) on one side and is infinite on the other side.

Angle

An angle is formed by two semi-straight lines with same vertex .

Straight angle

A right angle is an angle which has the same shape as angles in squares or rectangles.

Parallel, perpendicular lines

Two straight lines are parallel if they never intersect.
Two straight lines are perpendicular if they intersect with a right angle.
 The yellow lines are parallel the green lines are perpendicular

The parallelogram

 A parallelogram is a 4-edges figure with parallel opposite edges.

Some triangles

 Right-angled triangle Isosceles triangle Equilateral triangle A right-angled triangle is a triangle with a right angle An isosceles triangle is a triangle with two edges of the same length An equilateral triangle is a triangle with three edges of the same length