## anonymous one year ago The image shows a portion of a bridge supported by vertical pillars from the slope below. What is the length of the bridge between pillar B and pillar C?

• This Question is Open
1. anonymous

2. anonymous

Use pythagoras theorem for this question, both of em are similar triangles

3. anonymous

I honestly do not know how to.

4. anonymous

5. anonymous

and i dont run csi enhancer

6. anonymous

do you know how to do the process you were talking about ? could you explain to me how to ?

7. anonymous

ok lets start by finding this angle|dw:1438434416019:dw|

8. anonymous

29 feet 48 feet 56 feet 60 feet those are my options btw. And alright.

9. anonymous

$\cos^{-1} (\frac{ 40 }{ 50 }) is the \angle$

10. anonymous

cos^1 (40/50) is the angle

11. anonymous

im really confused.

12. anonymous

|dw:1438434482105:dw|

13. anonymous

okay from a to b on the top is 40 feet, bottom is 50 feet. and b to c on bottom is 70 feet, does that help ?

14. anonymous

$\frac{ 50 }{ 120 } = \frac{ 40 }{ 40+x }$

15. anonymous

now you can solve for x

16. anonymous

you can do that i hope

17. anonymous

i got 80 .. i feel like im wrong ... I havent had a math class since my freshman year in high school, and this is my senior year, and i just honestly dont have any idea what im doing ... i feel really stupid right now.

18. anonymous

lemme try solving$\frac{ 50 }{ 120 } = \frac{ 40 }{ 40+x }$$50 = \frac{ 4800 }{ 40+x }$$50(40+x)=4800$$2000+50x=4800$$50x=2800$$x=56$

19. anonymous

thank you ... But can i ask how you did that process ? if its too much to explain thats fine.

20. anonymous

alright you just cross multiple the denominator to each sides to cancel them out (the 1st 2 lines).

21. anonymous

cause fractions are messy. then you move the constant to one side of the equation (3rd line), by minus-ing the constant (2000) from both sides.

22. anonymous

thats how we end up with 50x=2800

23. anonymous

This whole thing confuses me. I literally feel dumb. I don't understand any of this.

24. anonymous

which part you do not understand?

25. anonymous

All of it... I don't even have a teacher, like i have to teach myself all of this stuff. Im probably wasting your time honestly, I cant comprehend this kind of stuff.

26. anonymous

ok ill write it in simpler form

27. anonymous

You don't have to do that..

28. anonymous

you gotta know how we come out with that first....

29. anonymous

otherwise you will keep getting stuck

30. anonymous

I just dont want to waste your time. And i don't think ill ever understand this.

31. anonymous

well just take it easy, 1 thing at a time

32. anonymous

okay..

33. anonymous

ill explain to you how the$\frac{ 50 }{ 120 } = \frac{ 40 }{ 40+x }$ is made first

34. anonymous

the triangle in the diagram is a similar triangle, therefore they are proportional to each other|dw:1438436528358:dw|

35. anonymous

okay

36. anonymous

50+70 is how we got the 120., and we take the ratio of the smaller triangle to the larger one

37. anonymous

ratio ?

38. anonymous

yea the fraction you saw 50/120 is the ratio

39. anonymous

okay.

40. anonymous

now the other side of the triangle is 40 on small side and 40+x on larger side

41. anonymous

they have to be proportional because they are co-linear so the ratio (that fraction) must be equal

42. anonymous

okay.

43. anonymous

you can understand that?

44. anonymous

i think.

45. anonymous

lemme try draw something to show you what i mean|dw:1438437049240:dw|

46. anonymous

okay

47. anonymous

like this in case the ratio of the triangle is 1:2 or 1/2

48. anonymous

its similar as the question you had but the proportion is not so straightforward

49. anonymous

so we use the ratio to find the distance of 40+x, with the ratio of the 50/120

50. anonymous

I have to go. Can we finish this later ?

51. anonymous

sure and see ya!

52. anonymous

okay , thank you. i gave you a medal.

53. anonymous

thank you

54. anonymous

no problem.