Two Plus Two Newer Archives  

Go Back   Two Plus Two Newer Archives > Other Topics > Science, Math, and Philosophy

Reply
 
Thread Tools Display Modes
  #1  
Old 11-30-2007, 02:30 PM
valenzuela valenzuela is offline
Senior Member
 
Join Date: Dec 2004
Location: Santiago, Chile
Posts: 6,508
Default Geomerty question


The black dot is the centre of the circunference btw.

Is the blue angle equal to the sums of the green angle and the red angle? My textbook says it is but I dont see how can that be? [img]/images/graemlins/frown.gif[/img]
Reply With Quote
  #2  
Old 11-30-2007, 02:54 PM
madnak madnak is offline
Senior Member
 
Join Date: Aug 2005
Location: Brooklyn (Red Hook)
Posts: 5,271
Default Re: Geomerty question

Level?
Reply With Quote
  #3  
Old 11-30-2007, 03:00 PM
valenzuela valenzuela is offline
Senior Member
 
Join Date: Dec 2004
Location: Santiago, Chile
Posts: 6,508
Default Re: Geomerty question

no...but now I know why the blue angle = red + green
Reply With Quote
  #4  
Old 11-30-2007, 04:09 PM
jay_shark jay_shark is offline
Senior Member
 
Join Date: Sep 2006
Posts: 2,277
Default Re: Geomerty question

Angle green = angle pink since it is subtended by the same chord . (ie , the chord formed from the vertices of the green angle and yellow angle )

So we require to show that the blue angle = the pink angle + the green angle . But this follows from the exterior angles theorem .
Reply With Quote
  #5  
Old 11-30-2007, 04:45 PM
_Z_ _Z_ is offline
Senior Member
 
Join Date: Jul 2004
Posts: 356
Default Re: Geomerty question

[ QUOTE ]
Angle green = angle pink since it is subtended by the same chord . (ie , the chord formed from the vertices of the green angle and yellow angle )


[/ QUOTE ]

Green and pink are not necessarily equal.

You meant to say:

Angle green = angle yellow since they are subtended by the same chord.


So it is sufficient to show that blue = yellow + red.

Z
Reply With Quote
  #6  
Old 11-30-2007, 07:58 PM
jay_shark jay_shark is offline
Senior Member
 
Join Date: Sep 2006
Posts: 2,277
Default Re: Geomerty question

[ QUOTE ]
[ QUOTE ]
Angle green = angle pink since it is subtended by the same chord . (ie , the chord formed from the vertices of the green angle and yellow angle )


[/ QUOTE ]

Green and pink are not necessarily equal.

Z

[/ QUOTE ]

I think it's clear when I say that the angles are equal because it is subtended by the same chord . It is very easy to show that blue = yellow + red since the sum of the angles of a triangle is 180 .
Reply With Quote
  #7  
Old 11-30-2007, 08:47 PM
Enrique Enrique is offline
Senior Member
 
Join Date: Mar 2005
Location: Mexico
Posts: 621
Default Re: Geomerty question

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
Angle green = angle pink since it is subtended by the same chord . (ie , the chord formed from the vertices of the green angle and yellow angle )


[/ QUOTE ]

Green and pink are not necessarily equal.

Z

[/ QUOTE ]

I think it's clear when I say that the angles are equal because it is subtended by the same chord . It is very easy to show that blue = yellow + red since the sum of the angles of a triangle is 180 .

[/ QUOTE ]

You wrote angle green = angle pink.
That statement is false. Although you give the explanation about angle green and angle yellow opening the same chord, hence angle green = angle yellow. And now you can say angle blue = angle yellow + angle red
Reply With Quote
  #8  
Old 11-30-2007, 10:44 PM
BaldElephant BaldElephant is offline
Member
 
Join Date: Oct 2007
Posts: 34
Default Re: Geomerty question

Hmm, it's clear that:
g+p=b

and

y+r=b

But, I don't know how to get b=g+r
Reply With Quote
  #9  
Old 11-30-2007, 10:48 PM
jay_shark jay_shark is offline
Senior Member
 
Join Date: Sep 2006
Posts: 2,277
Default Re: Geomerty question

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
Angle green = angle pink since it is subtended by the same chord . (ie , the chord formed from the vertices of the green angle and yellow angle )


[/ QUOTE ]

Green and pink are not necessarily equal.

Z

[/ QUOTE ]

I think it's clear when I say that the angles are equal because it is subtended by the same chord . It is very easy to show that blue = yellow + red since the sum of the angles of a triangle is 180 .

[/ QUOTE ]

You wrote angle green = angle pink.
That statement is false. Although you give the explanation about angle green and angle yellow opening the same chord, hence angle green = angle yellow. And now you can say angle blue = angle yellow + angle red

[/ QUOTE ]

It was a typo . Thx for clearing that up .
Reply With Quote
  #10  
Old 11-30-2007, 10:53 PM
TWCReborn TWCReborn is offline
Junior Member
 
Join Date: Nov 2007
Location: Los Angeles
Posts: 16
Default Re: Geomerty question

These types of problems are very simple. Ignore the circle in the beginning. Two properties are used:
1.) Two angles forming a straight angle are supplementary angles. Basically this means when there are two angles side by side on a straight line, they add up to 180 degrees.
2.) The 3 angles on a triangle add up to 180 degrees.

The rest is just algebra. Label each relevant angle x, y, z, etc. Write out relationships that you find. Combine equations to show your desired equality.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 11:58 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.