Question

In the figure below, EC || AB. Find the length of DE.
A. 2
B. 4
C. 6
D. 8

Answer 1

@phebe

Answer 2

use ratio

Answer 3

ratio? how so? i'm just really not great with geometry..
@mokeira

Answer 4

Basically, the common sides of those triangles, when you divide them, will equal the same answer every time. So you have a large triangle ADB and a small triangle EDC. Because these two triangles are congruent, I can take the length of the left side of ADB (which would be side AD) and divide it by the length of left side of EDC (which would be ED). When I divide these two left sides, I will get a value that is the same as if I divided the two lengths of the bottom sides of those triangles, which will also be equal to the division of the lengths of the right sides of those triangles.

So for triangle ADB, the length from D to B is given as 12+8 = 20. This would be the right side of that triangle. For the smaller triangle EDC, the length of its right side, from D to C is given as 12. So if I divide those two sides, I get 20/12 = 5/3.
If I do the same thing with the two bottom sides and the two left sides, I should get 5/3 every time.

For the triangle ADB, the length of the left side, A to D, is given to be 10. So the value the problem wants is the length of the left side of the triangle EDC, so the length of E to D (or D to E, same thing). The division of these two left sides needs to equal 5/3. So because of this, I have 10/DE = 5/3. So using this ratio, solve for DE. If that makes any sense.

Answer 5

Hm, I think I understand what you're saying so it has to equal to 5/3

Answer 6

it says to find the lenth of DE an to mee in the graph it looks like the line stops halfway soo half of 10 is 5, you can solve from there XD