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November 13th, 2015, 05:56 AM  #1 
Newbie Joined: Nov 2015 From: India Posts: 14 Thanks: 1  Are angles in similar triangle in the same proportion as the sides?
Are angles in similar triangle in the same proportion as the sides? What I mean is, if I consider triangles ABC and DEF, where AB:DE=1:2 then is angle C:angle F also 1:2? Last edited by skipjack; November 13th, 2015 at 05:59 AM. 
November 13th, 2015, 06:00 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 19,983 Thanks: 1853 
In general, no. As the triangles are similar, angles C and F are equal.

November 13th, 2015, 08:10 AM  #3 
Math Team Joined: Jan 2015 From: Alabama Posts: 3,261 Thanks: 894 
The crucial point is that, unlike the sides, the three angles in a triangle must add to 180 degrees. While the sides of one triangle might be 1/2 the sides of the other, the angles cannot be 1/2 the angles of the other since, then, they wouldn't add to 180 degrees.

November 13th, 2015, 03:37 PM  #4 
Newbie Joined: Nov 2015 From: India Posts: 11 Thanks: 2 Math Focus: multivariable calculus and Euclidean geometry 
Ok....so think of it this way... you know what zoom is right? Two similar triangles are made by zooming one so they have the same angles but the sides magnify/diminish by the same ratio, say all the sides are now .5 times the original ones or twice as large. Answer to your question is no btw since angles are in ratio 1:1 and sides are in a ratio that has nothing to do with the angles.
Last edited by skipjack; November 14th, 2015 at 12:51 AM. 
November 13th, 2015, 05:58 PM  #5 
Newbie Joined: Nov 2015 From: India Posts: 14 Thanks: 1 
Wait, my question was different. They are similar triangles so corresponding angles will be equal. I'm gonna edit my question. I actually combined two questions from my notebook. Can't I edit my question? Last edited by skipjack; November 14th, 2015 at 12:47 AM. 
November 13th, 2015, 06:17 PM  #6 
Newbie Joined: Nov 2015 From: India Posts: 14 Thanks: 1 
I made some mistake in identifying my queation. lol I meant something else. How can I edit my question? Last edited by skipjack; November 14th, 2015 at 12:48 AM. 
November 13th, 2015, 09:29 PM  #7 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,885 Thanks: 1088 Math Focus: Elementary mathematics and beyond 
You can't. Post your question below. 
November 14th, 2015, 08:23 PM  #8 
Senior Member Joined: May 2015 From: Varanasi Posts: 110 Thanks: 5 Math Focus: Calculus 
Not necessarily. If they are then they must be called as congruent triangle. Similar means similarity in shape and not in size, so similar means angles are similar and not the length of sides. A congruent triangle is similar but similar may not be congruent.


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angles, proportion, sides, similar, triangle 
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