## alainabbyboo22 3 years ago Calculate the length of AD given AB = 7 cm, AC = 25 cm, and AE = 35. A. 3.5 cm B. 5 cm C. 25 cm D. 50 cm

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1. alainabbyboo22

2. alainabbyboo22

@nubeer

3. nubeer

ok can't figure out this one.

4. nubeer

sorry.

5. JakeV8

The numbers given in the problem and the diagram you posted don't seem to go with the answer choices. I'm also not sure how to solve this one, but something seems mixed up also...

6. alainabbyboo22

that's what the choices are for this question /:

7. JakeV8

yeah, I'm not doubting you... I just don't know what to do with the situation.

8. tcarroll010

9. tcarroll010

10. JakeV8

how did you know to set up a ratio of the short portion of one leg to the whole length of the other leg?

11. tcarroll010

There is a good website explaining all this. Look at example 2: http://www.pinkmonkey.com/studyguides/subjects/geometry/chap7/g0707701.asp

12. tcarroll010

It goes with figure 7.21b which is the figure on the right.

13. tcarroll010

They use different letters for their points, so you have to rewrite the letters, but its almost the exact same problem.

14. tcarroll010

It's corresponding sides of similar triangles

15. JakeV8

Very nice... I was thinking ratios for similar triangles, but I didn't catch the fact that the "slanted" base and midsections would cause the ratios to be different. Thanks for the link... my goal of "learn something new daily" has been met :)

16. tcarroll010

This is sort of obscure, but geometry is way under-rated. Excellent way to build logic.

17. tcarroll010

18. tcarroll010

In that website that I referenced, they alluded to properties of the cyclic quadrilateral and that might have left some here a little empty like it was magic "balck box" stuff. One really has to come to grips with the cyclic quadrilateral first, so here's another website that explains why I could use that ratio: http://www.onlinemathlearning.com/quadrilateral-circle.html

19. tcarroll010

It's a video (near the bottom) called "Proof for the Cyclic Quadrilateral"