<p>can ya guys help me out w/ this problem? its easy but im having a brain fart at the moment. </p>
<p>Its from the oct 05 test. In triangle ABC, AB= AC, E is midpoint of AB and D is the midpoint of AC. If AE = x and ED = 4, what is the length of BC?</p>
<p>Thanks.</p>
<p>i did this few days ago,
the 2 triangles are similar. if u draw it separately , u can see that the other one is a larger version.
i think they r called similar triangles, meaning they have same angles for all 3.
this means the sides of the triangles are proportional.
there is a certain ratio...</p>
<p>nuff said, =)</p>
<p>ah right thanks</p>
<p>So whats the answer? i got 4</p>
<p>BC is 8 i think.</p>
<p>Oh yeah. Forgot to x2. What was your method ren? I sorta just assumed that the side ED is a side of a triangle that is 1/4 of the larger, then i just found the area then X4 to find the area of the larger 30-60-90 triangle and then the sides. I don't get how you can use proportions in that one, they only give you one side. it would be awesome if you can show me how you would use proportions on these questions.</p>
<p>in the above question ABC is an isosceles triangle and ED is the line joining the midpoints of the equal sides i.e. AB and AC. Knowing this we can either</p>
<p>1.Use the theorem tht the line joining the midpoints of the two equal sides of an isosceles triangle is half the length of the base and is parallel to it.
So, frm this we can say
ED=BC/2
BC=2*ED=8</p>
<p>2 Or u could use the method described in post#2
i.e
triangle AED~triangle ABC
AE/AB = AD/AC = ED/BC
AE/AB = ED/BC
x/2x = 4/BC [AE=x and E is the midpoint of line AB.Hence,AB=2AE=2x]
1/2=4/BC
BC=4*2=8</p>
<p>yeah ^something like that, similar triangles u can always set up something like:
x/y = 2x/?y
make sure the sides are the same,regardless of the length of the side. remember, they're similiar, so theres always a proportionality.</p>