Prove that the angle bisector theorem gives m(∠EAD)=[m(∠ABC)-m(∠ACB)]/2

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Qemikal
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Hi, guys, i made an exercise, can you prove this?
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m(∠EAD)=[m(∠ABC)-m(∠ACB)]/2
If you have 5 free minutes, try it, i hope you'll like it!
It's my first own exercise, so I would like some feedback, too.
AD= bisecting(splits angle in 2 equal sides)
 
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You can't prove this, it is, generally, not true. By choosing D at different places along BC, angle EAD can take on many different values while the right side, not depending on D, is fixed. Was there some other condition on D you did not give?
 
HallsofIvy said:
You can't prove this, it is, generally, not true. By choosing D at different places along BC, angle EAD can take on many different values while the right side, not depending on D, is fixed. Was there some other condition on D you did not give?
My bad, I forgot to add that AD splits the angle in 2 equal sides(angles).
 
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