**Created it, 05/10/15**

**Update it,
05/10/30**

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MATHEMATICAL FORMS “GEOMETRY” 1st PART

** FOOT- NOTE :** In these lessons with
for goal to represent and gather formulas, tables and graphs usable in
elementary calculations of geometry, physics and electronics.

They were conceived as of the memories assistances of reference to which one will be able to refer to solve problems relating to the calculation of the circuits. It is thus not necessary to remember exactly the formulas and the procedures of computation of the exposed subjects. It will be enough to only once carry out the calculations indicated in the examples to remember to the convenient period of the existence of a formula or a graph usable for the solution of a given problem. Indeed, even if one remembers only very vaguely procedure, it will be always possible to resort to these lessons of memories assistances where the formulas and graphs are indicated which will make it possible to solve the practical problems encountered in the work of the technician.

However, if you wish to be exerted with calculations, you will be able to at will make new exercises by working out them on the model of the examples deferred in these lessons of memories assistances.

To this end, it will be enough to replace the
numerical values of the example by other values chosen randomly and to carry out
the operations with the new data**;** in the more complex cases, you will be
able to check the exactitude of the final result with the evidence of arithmetic
calculation.

**To facilitate the reading of
these lessons of memories assistances, the formulas are numbered in an order
ascending, as well as the tables and graphs.**

Each formula is illustrated a practical example of application.

In general, one proceeds in the following way**:**
after having selected the formula, one replaces the letters of the second member
by the respective numerical values (given) and one carries out calculations to
obtain the final result. In the more complex cases, it will be indicated an
additional control which will be able to be added to the evidence of arithmetic
calculation.

Sometimes, it can prove to be advantageous to
replace ordinary calculation, i.e. numerical, by a known particular procedure
under the name of graphic method**;** therefore, in addition to the ordinary
calculation which derives directly from the formula, one will be able to
sometimes take into account also that carried out by the graphic method.

It can happen that one needs to know dimensions, surfaces or unspecified volumes of objects, and that when it is not easy, or even completely impossible, to take direct measurements. It is then necessary to carry out calculations.

For example, it can present cases where it is necessary to know the length of a whorl, the section of a driver, the section or the volume of a magnetic core…

In general, they are problems which one can quickly solve by applying a suitable formula of geometry.

We will thus find in this lesson of memory assistance the formulas of geometry having a practical application in electronics.

**
FORMULATE
1 -** Calculation
of the area of a triangle knowing the values of the base and height (figure
1-a).

**
FORMULATE 2
-** Calculation of the area of an equilateral triangle, “triangle
having three equal sides” (figure 1-b) knowing the length on the side.

**Example (figure 1-b) :**

**
FORMULATE 3
-** Calculation of the area of an
isosceles triangle “triangle having two equal sides” knowing the value on
the equal sides and the base.

**
FORMULATE 4
-** Calculation of the area of a scalene triangle “triangle having
three unequal sides” knowing the length on the sides.

In this formula “**p**”
indicates the half-perimeter, i.e. the half the sum on the three sides. **For
applying the formula, it is necessary to calculate separately the value “****p”
of the half-perimeter.**

**
FORMULATE 5
-** Calculation of the hypotenuse of a
right-angled triangle knowing the two other sides (the right-angled triangle is
a triangle having an angle of **90°;** the
hypotenuse is the largest side, the two other sides form the angle of **90°**).
(See the figure 1-e above).

**
FORMULATE 6
-** Calculation on a side of a
right-angled triangle knowing the lengths of the hypotenuse and other side (for
the significance of the terms, you defer to formula 5).

**
FORMULATE 7
-** Calculation of the area of a
right-angled triangle knowing the two sides of the right angle.

**
FORMULATE 8
-** Calculation of the diagonal of a square knowing the length on the
side. (Figure 2-a).

**
FORMULATE 9
-** Calculation of the area of a square knowing the length on the side.

**Example (figure 2-a) :**

**
FORMULATE 10
-** Calculation of the area of a square
knowing the length of the diagonal.

**Example (figure 2-a) :**

Data **: d**
**
70,70 mm** (approximate value established with formula 8)

Surface**: S**
**
70,70 ^{2} / 2 = 4 998,49 / 2 = 2 499,245 mm^{2}**

__Compare this result with that obtained by
applying formula 9__. The difference **in 0,755 mm ^{2}
(2 500 - 2 499,245 = 0,755)** is due to the introduction of the
approximate value

(To facilitate the reading, we defer the same figure below to knowing figure 2).

**
FORMULATE 11
-**
Calculation of the diagonal of a rectangle knowing the values of the base and
height.

(This formula above is similar to formula 5).

**
FORMULATE 12
-** Calculation of the area of a rectangle
knowing the values of the base and height.

**Example (figure 2-b) :**

**
FORMULATE 13
-** Calculation of the area of a rhombus knowing the length of the
diagonals (the rhombus is a quadrilateral having four equal sides and of the
unequal adjacent angles).

**Example (figure 2-c) :**

**
FORMULATE 14 -**
Calculation of the area of a
parallelogram knowing the values of the base and height.

**b = bases**

(This formula above is similar to formula 12).

**Example (figure 2-d) :**

**
FORMULATE 15 -
** Calculation of the area of a
trapezoid knowing the values of the two bases and height.

**
FORMULATE 16 -** Calculation of the area of a
regular pentagon knowing the length on the sides (the regular pentagon is a
polygon having five equal sides and five equal angles).

**Example (figure 3-a) : **

**
FORMULATE
16 - 1
: Regular
and irregular polygons**

It is said that a **polygon**
is **regular** when all its sides and all its
angles are adequate (equal).

It is said that a **polygon**
is **irregular** when certain on its sides and
some of its angles are unequal (incongruous).

**Regular polygon
Irregular polygon**

**
FORMULATE 17 -**
Calculation of the area of a
regular hexagon knowing the length on a side (the regular hexagon is a polygon
having six equal sides and six equal interior angles).

**Example (figure 3-b “above”)
**

**
FORMULATE 18 -** Calculation of the perimeter
of a circle (circumference) knowing the value of the diameter.

**
FORMULATE 19 -**
Calculation of the area of a
circle knowing the value of the diameter.

**
FORMULATE 20 -**
Calculation length of an arc
of circle knowing the value of the angle in the center and the length of.

(To facilitate the reading, we defer the same figure to knowing figure 3)

**
FORMULATE 21 -** Calculation of the area of a
circular sector knowing the value of the angle in the center and the length of
the ray (a circular sector is the plane surface delimited by an arc of circle
and two rays).

**
FORMULATE 22 -** Calculation of the area of a
circular ring knowing the value of the two diameters (a circular ring is the
plane surface ranging between two concentric circumferences).

**
FORMULATE 23 -**
Calculation of the area of a
segment of parabola knowing the value of the base and height (one calls segment
of parabola the plane surface ranging between an arc of parabola and the cord
underlain between the ends of the arc).

**
FORMULATE 24 -** Calculation of the area of an
ellipse knowing the length of the two axes.

**
FORMULATE 25 -** Calculation length of a
propeller knowing the number of whorls, the values of the diameter and height.

**
FORMULATE 26
-**
Calculation of the volume of a cube knowing the length of the edge.

**a = edge **

**Example (figure 5-a) :**

**
FORMULATE 27 -** Calculation of the volume of
a parallelepiped knowing the values length and width of the base, and the height.

**a = length of the base has**

**
FORMULATE 28 -**
Calculation of the volume of
a cylinder knowing the values of the diameter and height.

**FORMULATE 28 - 1:** To
calculate a cylinder of a volume generated by the rotation of a rectangle around
one on its sides (**side surface = 2Rh ; total
surface = 2R (h + R) ; volume = R²h**, **h
being the height** and **R the radius of the
basic circle**).

**
FORMULATE 29 -**
Calculation of the volume of
a hollow roll knowing the values of the two diameters and height.

**
FORMULATE 30 -**
Calculation of the volume of
a ring with square section knowing the values of the external diameters and
interns.

**
FORMULATE 31 -**
Calculation of the volume of
a torus (ring with circular section) knowing the value of the diameter external
and that of the diameter of the section of the ring.

**
FORMULATE 32 -**
Calculation of the area of a
sphere knowing the value of the diameter.

**
FORMULATE 33 -**
Calculation of the volume of
a sphere knowing the value of the diameter.

**
FORMULATE 34
-** Calculation of the area of a
segment of a sphere knowing the values of the diameter of contour and height.

**
FORMULATE 35 -**
Calculation of the volume of
a segment of a sphere knowing the value of the diameter of the base and height.

**
FORMULATE 36
-** Calculation of the volume of a
paraboloid knowing the value of the diameter of the base and height.

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