Proving Triangles Help

G

Guest

Guest
How do u know what theorems to use when proving triangles? I am so confused I know it's fairly simple but I failed my test and need major help in this area. Maybe could u start from the beginning because obviously I'm not getting it.
 
We can't repeat what it took a couple chapters to cover in a post. Show a problem and what you have tried.
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Gene
 
triangle4.gif


could u help me with this one?

but make midpoint D

I have to prove <B=<C
 
I think my problem is I don't understand the theorems very well
 
so AD=CD: because it's a definiton of midpoint right?
<BDA=<CDA: no clue
AD=AD: reflexive property?
triangle ABD congruent triangle ACD : ASA?
 
That's much better but there must be more to it. Like b = a*sqrt(3) or CD = a*sqrt(3)?
----------------
Gene
 
my text has this:

Given:AD is perpendicular to BC, D is the midpoint of BC.
Prove:<B=<C

then it has a triangle (similar to the image) with BD and DC the same
<D is 90 degrees
 
th_rightangle.jpg


That is exactly how the text shows (with mid line in exact center however)
 
Are you sure it isn't prove <A = <B?.
If a=1 and b=100 <B is definitly not =<C
 
<A cannot be equal to <B because itriangle BAD is not isoceles it is a right angle triangle therefore all 3 angles in triangle BAD are different
 
There was no mistake it's in my book in print to prove <B is equal to <C which it is.
for BD equals DC
 
it's supposedly not suppose to be complicated I'm only in math 20 pure grade 11
 
I see what you mean now I was referring to the second image I posted but if your looking at the first one it would be prove <A is equal <B
 
SLOW DOWN! Think about what you are doing, then post. You have switched A and B.
so AD=CD: because it's a definiton of midpoint right?
<BDA=<CDA: no clue
AD=AD: reflexive property?
triangle ABD congruent triangle ACD : ASA
Click to expand...

<BDA=<CDA right angles
triangle ABD congruent triangle ACD : SAS
<B=<C corresponding angles
You got it.
 
I don't quite understand how you know if a triangle is proved by ASA, SAS, or SSS
 
Because you said
AD=CD
<BDA=<CDA
AD=AD
That's two sides and the included angle. SAS
 
4hgurly said:
how do u know it's SAS?
Click to expand...

You were given that AD | BC. From that you can say that /BDA ~/CDA because perpendicular lines form right angles and all right angles are congruent. One pair of congruent ANGLES.

You were given that D is a midpoint, so you know that BD = CD . One pair of congruent SIDES.

You used the property of reflexivity to show that AD = AD ... another "pair" of congruent SIDES. Since the two pairs of sides are the legs of the right angles, that's SAS (sides with the angles formed in between)

I hope that helps you.
 
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