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# Geometry Proof Help

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3 Could one of this site's math Wizards please help me with this. The teacher wants me to make a 2 column proof that proves this and I am kind of stuck. The topic for this week is triangle inequailities.

Apr 14, 2019

#1
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(1) AB = AC                                      Given

(2) Angle ABC = Angle ACB             In a triangle, angles opposite equal sides are also equal

(3) Measure of Angle ACB =            Exterior Angle Theorem

(4) Measure of Angle ACB >         Consequence of (3)

(5) Measure of Angle ABC >        Substitution

(6) Measure Angle B >                By (5)

Measure Angle D   Apr 14, 2019
edited by CPhill  Apr 14, 2019
#2
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Thank you for this but I have one question. How is your step 3 the Alternate Exterior Angles Theorem? I do not understand how you got that and I was wondering if you could elaborate.

OkNietzsche  Apr 14, 2019
#3
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OK...note that

mAngle ACB  + mAngle  ACD  = 180°     (1)

And

So

(1) = (2)  so

mAngle ACB + mAngle ACD  =  mAngle CAD + mAngle ADC + mAngle ACD

Subtract  mACD from each side

So   