Plane Figures: Formulas and How to Recognize Them

How to recognize plane figures. Diagram, examples and formulas to calculate the area of the main geometric figures and polygons.Plane figures are geometric figures – also called polygons – that occupy a flat surface.

Why is it important to recognize them?

Because they are the basis for being able to solve problems that also have solids as protagonists .

PLANE FIGURES WHAT ARE THEY?

Here is a list of the main plane figures:

The square
is a polygon made up of four sides, completely equal and forming four 90° angles.
The rectangle
It is formed by four sides, parallel and equal in pairs. The two bases (the upper one and the lower one) are parallel to each other, and so are the two altitudes (the right one and the left one). The rectangle also has four 90° angles.
The circle
It is a polygon made up of a circumference , or a line that closes the circle itself. The line that divides the circle into two perfectly equal parts and that passes through the center is called the diameter . Half of the diameter is called the radius (so for example, if the diameter measures 8 cm, the radius measures 4 cm).
The triangle
It is a polygon that has only three sides, but the measures of the angles vary depending on the type of triangle. For more information, see the next paragraph.
Parallelogram (or parallelogram)
It is a polygon with opposite sides parallel. The opposite sides and angles of a parallelogram are congruent.
The rhombus
It is an equilateral parallelogram. It also has two perpendicular diagonals that intersect at the midpoint. The opposite angles are congruent, that is, they have the same size, while the angles adjacent to each side are supplementary, with a sum equal to 180°.
Other polygons
Trapezoid, pentagon, hexagon, octagon… depending on the number of sides these polygons take different names.

PLANE FIGURES: THE TRIANGLE

A separate paragraph, we were saying, deserves the triangle. This flat geometric figure can in fact be found under three different typologies, depending on the type of angles and sides:

Equilateral triangle
It has all three sides and angles equal. The latter measure 60° each (remember that the sum of the internal angles of a plane figure must always be 180°!);
Isosceles triangle
It has two equal oblique sides and a base of different measures. The two base angles measure 75° each, while the vertex angle measures 30°;
Scalene triangle
All three sides are of different lengths. The measures of the interior angles are also different.
Right-angled triangle
So called because the two legs form a right angle of 90°, while the other two angles formed by the hypotenuse measure 30° and 60°.