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Download "Доказательство тригонометрических тождеств Пифагора"

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00:00:00
Hello and welcome to another video of easy matte in this video we are going to demonstrate some
00:00:06
trigonometric identities specifically we are going to demonstrate the Pythagorean trigonometric identities
00:00:13
these three trigonometric identities are called thus the one that relates to the sine and the tangent
00:00:19
and secant cosine and ccoo tangent and co secant To demonstrate these identities, we are going to start
00:00:24
with the first one, which is the most elementary, the one that is used the most, which tells us that sine squared
00:00:30
theta plus cosine squared theta is equal to 1 for any real number theta. Well, I
00:00:38
will demonstrate this identity. In two ways we are going to start with the classic proof that has
00:00:44
to do with a right triangle, which is how we start by defining the sine and the sine and then we will
00:00:50
extend the proof to include more angles than can be built in
00:00:56
a triangle, then we go to start with a right triangle like this one here we are going to
00:01:03
write the angle theta in one of these two angles the east of here remember it is the angle
00:01:09
of 90 degrees is often represented as a cuadradito then we will choose as angle
00:01:14
theta one of these two'll put this one here it will then be our theta angle and
00:01:21
let's remember what are the definitions of the sine and the cosine the sine of an angle from
00:01:27
a right triangle is defined as the opposite leg on the hypotenuse while the cosine
00:01:33
of the angle is defined as the adjacent leg between the hypotenuse let's quickly remember
00:01:39
how it is that The sides of the triangle are called as we said this here the angle of 90 degrees and
00:01:46
this angle is formed by these two sides, these sides are called legs while the third side
00:01:52
that is the largest of the right triangle is called hypotenuse now well if we choose
00:01:58
as our theta angle is from here then the leg that is next to the theta angle is
00:02:04
called the adjacent leg while the leg that is in front of the theta angle it is called opposite
00:02:11
leg, well with that in mind we can start with the demonstration and for that we are going to suppose that
00:02:18
this right triangle has hypotenuse 1 we are going to put it like this for simplicity then we say that
00:02:25
the hypotenuse of this triangle is 1 now to the other two sides of the triangle we are going to put variables
00:02:32
in them we are going to say that this side measures x and we are going to say that this side measures y we could
00:02:40
put any other letter but well the usual thing is to put x and now using these formulas we have
00:02:48
that the sine of the angle theta will be opposite legs on hypotenuse that is to say it will make
00:02:54
between 1 then sine of theta is since it is the opposite leg on the hypotenuse that is worth 1
00:03:03
I have divided by 1s simply and when we divide a number by 1 it gives us exactly
00:03:09
the same then we leave it directly as ye we do the same with the cosine cosine of theta it
00:03:15
will be adjacent leg which in this case adjacent leg is x divided by hypotenuse which is 1
00:03:23
and again here x between e 1 is simply x now what we are going to do is use the
00:03:31
pythagorean theorem the pythagorean theorem remember that it tells us that the hypotenuse squared is equal
00:03:39
to the sum of the squared legs so in this case the legs are x and so If
00:03:47
we square them and add them that gives us the result of the hypotenuse squared which
00:03:53
is the 1 squared good then we have that x squared more than squared is equal to 1 squared
00:03:59
but from what we obtained up here sine of tts cosine of theta is x so we substitute here
00:04:07
instead of x we ​​put cosine detect instead of we put sine so we have that cosine
00:04:13
squared of theta plus sine squared of theta is equal to 1 squared which is simply one
00:04:19
is from here is the Pythagorean identity, although in this case the sine appears first and then
00:04:25
the cosine, because remember that the sum does not matter the order in which we do it, it is the same to put
00:04:31
the cost first and then the sine than first the sine and then the cosine because they
00:04:35
are finally being added with this from here we have demonstrated the first of the Pythagorean
00:04:40
trigonometric identities and we see why they are called like that because they arise precisely from the Pythagorean theorem but
00:04:47
notice something here this angle theta is an angle of the right triangle and remember that The three
00:04:54
angles of a triangle add up to 180 degrees, we already have an angle of 90 here, therefore
00:05:01
this angle plus this angle must add another 90 so that the three give us 180 that means that
00:05:07
this angle theta cannot be an angle greater than 90 degrees. because this more this here should
00:05:14
give us 90 then this idea we have just demonstrated but only for angles that are greater
00:05:21
than 0 and less than 90 degrees, however we can demonstrate the identity for any angle both
00:05:28
positive or negative and it can therefore be a greater angle Let 90 or any real number, we are going
00:05:35
to do that proof, but for that we must remember the definition of sine and cosines
00:05:40
for any angle. Then we are going to start by remembering that definition, the definition of sine
00:05:47
and cosine for any angle is made from a circle, we start by drawing our
00:05:55
Cartesian plane, we have the x-axis and the y-axis and we draw a circle centered on the
00:06:01
origin that has radius 1, then if we We draw an angle here, always starting to measure
00:06:08
it from the positive x axis, for example this angle here this angle begins to be measured from
00:06:15
the positive x axis and ends here, do not give this blue point, we are going to call that angle theta
00:06:22
then this point in blue It is a point of the Cartesian plane, we are going to call it py, it has
00:06:28
its coordinates x comma, then the sine of the theta angle is defined as the y-coordinate and
00:06:36
the cosine of the theta angle as the x-coordinate, that is, the cosine of theta is equal to the sine of theta is
00:06:43
equal. a and e that is to say that if we draw here any angle on the circumference knowing
00:06:49
the coordinates of that point we can determine the cosine of the angle that s e formed and the sine of the
00:06:55
angle that was formed well this is simply to remember the definition of sines and cosines for
00:07:01
any angle I presented here the angle in the first quadrant but we could
00:07:07
draw the angle in any other quadrant and the definition is still valid Well with this in
00:07:14
mind we must remember what is the equation of a circle of radius 1 centered at the origin the
00:07:23
equation of a circle of radius 1 and center at the origin, that is, at 0 0 is x squared plus and
00:07:29
squared equal to 1 well here if we know that x is the cost not sucking and breast boob to the
00:07:38
substitute here on Xs and air because we have again the Pythagorean identity good is here
00:07:44
to remember that the equation of the circle is obtained by applying the Pythagorean theorem and that is
00:07:52
why this identity is called the Pythagorean identity, it must be remembered that the equation of
00:07:58
the circumference is obtained from calculating all the points in the Cartesian plane whose distance
00:08:05
to the origin n is equal to 1 and to calculate that distance is that the Pythagorean
00:08:10
theorem is used that I will explain in some other video in which we will find the equation of
00:08:16
circumference for any radius and any good center so with this we have already demonstrated
00:08:23
the first Pythagorean identity for any angle because in this case we can already represent
00:08:28
positive angles and negative angles of any value and we still need to prove two more Pythagorean
00:08:35
Pitot identities but those other two identities already emerge very quickly. From
00:08:41
here we are going to start. demonstrating the first of those identities for that what we are going to do is
00:08:47
divide this identity which is finally an equation we are going to divide it by cosine
00:08:53
squared of theta that means that each term of the equation we are going to divide by cosine
00:09:00
squared of theta then we have square sine of t is divided by square cosine of theta
00:09:07
then square cosine of t is divided by square cosine of theta and on the other side of the
00:09:12
equal sign we have 1 divided by square cosine of theta and now we are going to use the following that
00:09:20
is not detected between cosine of theta is equal to tangent and that 1 enzo the non-theta cost is equal
00:09:25
a secant beteta then here as we have sine between cosine that will be tangent but since
00:09:32
the trigonometric functions are squared then this will give us tangent to the square of theta
00:09:38
then here we have squared cosine between squared cosine as we are dividing the same quantity
00:09:43
by the same amount because that gives us equal to 1 and on the right side we have one between the cosine
00:09:49
one between cost is not secant and since it is squared of the cosine because it will be secant
00:09:55
to the square and thus we have obtained the second of the Pythagorean identities for us A third
00:10:01
identity is missing and that we are going to obtain by dividing this identity by the square sine of theta
00:10:09
then again starting from this identity we are now going to divide by se not square of
00:10:16
theta each of the terms of the equation and we have the following sine squared between
00:10:22
0 squared then here cosine squared between sine squared and here one between sine squared and here
00:10:29
we are going to use now that they do not detect between sine of theta is co tangent of theta and
00:10:36
that one between the sine of theta is co secant of theta so here square sine of theta between
00:10:42
square sine of theta gives us 1 because we are dividing the a quantity by itself
00:10:48
that gives us 1 then cosine between sine as We said it is co tangent and since here they are
00:10:53
squared because it is with a square tangent of theta and then here one between squared sine
00:10:59
because as one between sine is with secant because we will be here with secant squared
00:11:05
then this is the third identity and so We have finished if you want to see other trigonometric
00:11:11
proofs in the description of this video you can find the link to the complete list
00:11:18
of proofs of trigonometric identities so I invite you to Let them see it and if you liked
00:11:25
this video, please support me by giving me a like, subscribe to my channel and share my videos
00:11:30
and remember that if you have any question or suggestion, you can leave it in the comments.

Description:

▼ ВАЖНО ▼ В этом видео я продемонстрирую 3 тригонометрических тождества Пифагора, квадратный синус плюс квадратный косинус, тангенс, котангенс, секанс, косеканс, используя прямоугольный треугольник, а также из определения единичной окружности в декартовой плоскости, все объяснено пошагово Он прошел. # тригонометрия # геометрия # демонстрация ---------- ** ВАЖНЫЕ ССЫЛКИ ** Курс тригонометрии: https://www.youtube.com/playlist?list=PL9SnRnlzoyX3kLYWUsrmrq0qy2Bye1JF4 Специальные видео: https://www.youtube.com/playlist?list=UUMOHwtud9tX_26eNKyZVoKfjA Обзорный курс математики (довузовской) https://www.youtube.com/playlist?list=PL9SnRnlzoyX1-FFtFcUupLSdnTRvs8B5K ---------- ** СМОТРЕТЬ ВСЕ МОИ КУРСЫ ЗДЕСЬ ** https://www.youtube.com/c/Arquimedes1075/playlists ---------- ** СПИСОК ИСПОЛЬЗУЕМОЙ ЛИТЕРАТУРЫ ** - Тригонометрия, Своковски Коул - Геометрия и тригонометрия, Baldor - Упрощенная математика, Конамат ---------- ** ПОЖЕРТВОВАНИЯ ** - Paypal: https://www.paypal.com/donate/ - Членство в каналах: https://www.youtube.com/channel/UCHwtud9tX_26eNKyZVoKfjA/join - Патреон: https://www.patreon.com/matefacil ---------- ** МОИ ДРУГИЕ КАНАЛЫ И СОЦИАЛЬНЫЕ СЕТИ ** - Канал по физике: https://www.youtube.com/channel/UCeFNpG-n8diSNszUAKaqM_A - Канал видеоигр: https://www.youtube.com/channel/UClSpw-rlRdygJmI33x1YagA - Twitch: https://www.twitch.tv/matefacil - Приложение MateFacil: https://educup.io/apps/matefacil - Facebook (Страница): https://www.facebook.com/unsupportedbrowser - Twitter: @Matefacilx - Instagram: @Matefacilx - Раздор: https://discord.com/invite/Gmb7sF9 ---------- # Math #tutorial #tutor #tutoriales #profesor ----

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