# Why is sin the y-coordinate on the unit circle?

Watch
Announcements

Page 1 of 1

Go to first unread

Skip to page:

I'm sure my question will be instantly misunderstood by most people in its current form, so I'll elaborate.

Basically, I mean why the specific

It makes sense, though, to have sine be the y-coordinate because of how the graphs look (y=sinx is the 'proper' wave and y=cosx looks like your usual wave shifted along). But is this how the names were chosen? Were the graphs plotted before the names were attributed?

I know this isn't really a mathematical question, but I've looked up the question and couldn't find any answers; I'm very curious to know.

Basically, I mean why the specific

*names*of the functions were chosen to be that way around. You would think, intuitively, that we would naturally attribute sine to the x-coordinate and COsine to the y-coordinate, just as we watch how y varies as we vary x on the Cartesian plane (by convention).It makes sense, though, to have sine be the y-coordinate because of how the graphs look (y=sinx is the 'proper' wave and y=cosx looks like your usual wave shifted along). But is this how the names were chosen? Were the graphs plotted before the names were attributed?

I know this isn't really a mathematical question, but I've looked up the question and couldn't find any answers; I'm very curious to know.

0

reply

Report

#2

(Original post by

I'm sure my question will be instantly misunderstood by most people in its current form, so I'll elaborate.Basically, I mean why the specific

**PrimeLime**)I'm sure my question will be instantly misunderstood by most people in its current form, so I'll elaborate.Basically, I mean why the specific

*names*of the functions were chosen to be that way around. You would think, intuitively, that we would naturally attribute sine to the x-coordinate and COsine to the y-coordinate, just as we watch how y varies as we vary x on the Cartesian plane (by convention).It makes sense, though, to have sine be the y-coordinate because of how the graphs look (y=sinx is the 'proper' wave and y=cosx looks like your usual wave shifted along). But is this how the names were chosen? Were the graphs plotted before the names were attributed?I know this isn't really a mathematical question, but I've looked up the question and couldn't find any answers; I'm very curious to know.As you can see, sin(θ) = y/1 = y

This is why the y-coordinate of that blue point of is the sin(θ) value, and this only works with the unit circle.

0

reply

Report

#3

(Original post by

Check out this picture ------>

As you can see, sin(θ) = y/1 = y

This is why the y-coordinate is the sin value.

**Dingooose**)Check out this picture ------>

As you can see, sin(θ) = y/1 = y

This is why the y-coordinate is the sin value.

0

reply

Report

#4

(Original post by

Do I smell Autograph?

**Alexion**)Do I smell Autograph?

0

reply

Report

#6

I laugh in the face of my maths teachers

0

reply

Report

#7

(Original post by

Well that looks significantly easier & nicer to use, and it's free...

I laugh in the face of my maths teachers

**Alexion**)Well that looks significantly easier & nicer to use, and it's free...

I laugh in the face of my maths teachers

0

reply

**Dingooose**)

Check out this picture ------>

As you can see, sin(θ) = y/1 = y

This is why the y-coordinate is the sin value.

It seems reasonable to say this, but there is a logical flaw in the argument. You are using the definition: sin(theta)=opposite leg / hypotenuse in a right-angled triangle.

But then you are defining the function sin insufficiently. You are only defining it for angles 0 to 90 (degrees), using your right-angled triangle definition. This is precisely why sin is defined via the unit circle definition - so that it is defined for all angles. And then that asks the question, why was sin defined as the y-coordinate of the terminal point?

0

reply

Report

#9

(Original post by

I thought someone would answer with this reasoning.

It seems reasonable to say this, but there is a logical flaw in the argument. You are using the definition: sin(theta)=opposite leg / hypotenuse in a right-angled triangle.

But then you are defining the function sin insufficiently. You are only defining it for angles 0 to 90 (degrees), using your right-angled triangle definition. This is precisely why sin is defined via the unit circle definition - so that it is defined for all angles. And then that asks the question, why was sin defined as the y-coordinate of the terminal point?

**PrimeLime**)I thought someone would answer with this reasoning.

It seems reasonable to say this, but there is a logical flaw in the argument. You are using the definition: sin(theta)=opposite leg / hypotenuse in a right-angled triangle.

But then you are defining the function sin insufficiently. You are only defining it for angles 0 to 90 (degrees), using your right-angled triangle definition. This is precisely why sin is defined via the unit circle definition - so that it is defined for all angles. And then that asks the question, why was sin defined as the y-coordinate of the terminal point?

0

reply

Report

#10

**PrimeLime**)

I thought someone would answer with this reasoning.

It seems reasonable to say this, but there is a logical flaw in the argument. You are using the definition: sin(theta)=opposite leg / hypotenuse in a right-angled triangle.

But then you are defining the function sin insufficiently. You are only defining it for angles 0 to 90 (degrees), using your right-angled triangle definition. This is precisely why sin is defined via the unit circle definition - so that it is defined for all angles. And then that asks the question, why was sin defined as the y-coordinate of the terminal point?

The unit circle definitions are an extension of the normal definitions, but they are based upon the normal definitions.

0

reply

Report

#11

(Original post by

TBH I'm seriously confused what you're trying to ask here. Except for the fact that most mathematical functions are defined as y=f(x), hence y=sinx, idekwya

**Alexion**)TBH I'm seriously confused what you're trying to ask here. Except for the fact that most mathematical functions are defined as y=f(x), hence y=sinx, idekwya

0

reply

Report

#12

(Original post by

Basically, I mean why the specific

It makes sense, though, to have sine be the y-coordinate because of how the graphs look (y=sinx is the 'proper' wave and y=cosx looks like your usual wave shifted along). But is this how the names were chosen? Were the graphs plotted before the names were attributed?

.

**PrimeLime**)Basically, I mean why the specific

*names*of the functions were chosen to be that way around. You would think, intuitively, that we would naturally attribute sine to the x-coordinate and COsine to the y-coordinate, just as we watch how y varies as we vary x on the Cartesian plane (by convention).It makes sense, though, to have sine be the y-coordinate because of how the graphs look (y=sinx is the 'proper' wave and y=cosx looks like your usual wave shifted along). But is this how the names were chosen? Were the graphs plotted before the names were attributed?

.

The word 'sine' is just an anglicization of a Latin translation of an Arabic corruption of a Hindu phrase meaning 'half-chord' - a long time ago, Indian scholars compiled tables of half-chord lengths corresponding to different angles at the centre of a circle. This half-chord length is what we recognize today as the y-coordinate of a point on the circle,

3

reply

(Original post by

Nothing to do with 'graphs' - trig functions were known about long before anyone even thought about graphs (certainly not before Descartes started thinking about coordinates!).

The word 'sine' is just an anglicization of a Latin translation of an Arabic corruption of a Hindu phrase meaning 'half-chord' - a long time ago, Indian scholars compiled tables of half-chord lengths corresponding to different angles at the centre of a circle. This half-chord length is what we recognize today as the y-coordinate of a point on the circle,

**davros**)Nothing to do with 'graphs' - trig functions were known about long before anyone even thought about graphs (certainly not before Descartes started thinking about coordinates!).

The word 'sine' is just an anglicization of a Latin translation of an Arabic corruption of a Hindu phrase meaning 'half-chord' - a long time ago, Indian scholars compiled tables of half-chord lengths corresponding to different angles at the centre of a circle. This half-chord length is what we recognize today as the y-coordinate of a point on the circle,

0

reply

X

Page 1 of 1

Go to first unread

Skip to page:

### Quick Reply

Back

to top

to top