The Student Room Group

Several co-geom problems

hi, i have no idea how to tackle these few questions. hoping someone could shed some light on them. any help is appreciated. thanks in advance.

Q. 3,4 left. thanks ^^
(edited 12 years ago)
For the first one, what's special about the triangle AND? Can you take it from there?
(edited 12 years ago)
Reply 2
if you still don't get it from ghostwalker's help, find AN using pythagoras. Thats the first step.
Reply 3
Original post by ghostwalker
For the first one, what's special about the triangle AND? Can you take it from there?


i only know that triangle DMN and AMN are congruent (SAS).
Reply 4
Original post by jackisalion
if you still don't get it from ghostwalker's help, find AN using pythagoras. Thats the first step.


o i get it. since triangle DMN and AMN are congruent (SAS), i could first find AN using Pyth. th. then AN=ND and use Pyth th. again to find out CD. am i right?
Reply 5
what exam board is this?
Original post by kingsclub
o i get it. since triangle DMN and AMN are congruent (SAS), i could first find AN using Pyth. th. then AN=ND and use Pyth th. again to find out CD. am i right?


Yep!
Reply 7
for the second one you find the vertical height of the large triangle in terms of its base & then use similar triangles to finish
Reply 8
Original post by the bear
for the second one you find the vertical height of the large triangle in terms of its base & then use similar triangles to finish


do i need to know the ratio of the 2 similar triangles? cause i dont know the smaller triangle's height...
Reply 9
once you have established the big triangle's height in terms of the base you will see straight away how tall the little triangle is

(PS the drawing is not to scale !! )
Reply 10
anyone's help for q.3 and 4?
Original post by kingsclub
anyone's help for q.3 and 4?


Q4. Difficult to just give a hint here. But, focus on the equiliteral triangle with a perpendicular dropped, and the ratio of lengths, also consider similar triangles.
Reply 12
Original post by ghostwalker
Q4. Difficult to just give a hint here. But, focus on the equiliteral triangle with a perpendicular dropped, and the ratio of lengths, also consider similar triangles.


can i say HD+BF = DB ?
Original post by kingsclub
can i say HD+BF = DB ?


Not without justification (and I'm not saying whether it's true or not there).

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