Posted by Joel on October 11, 2002 at 17:09:33:
In Reply to: Area problem posted by Bob on October 11, 2002 at 16:07:52:
: Huge triangle ABC has an area of 20,000,000 square feet.
: D is on AB, E is on BC and F is on CA.
: AD = 1/16th of AB, BE = 1/16th of BC, CF = 1/16th of CA.
: Find area of triangle DEF.
: Thank you.
I will get you started.
1. Draw a picture. Obviously you could put A, B and C anyplace, but it will be easier to see my explanation if we are both looking at the same picture. So, I put A at the top, B at the right end of the base, and C at the left end of the base. Now put D, E, and F as described in your problem. Next, drop a line from A, perpendicular to BC, meeting BC at point G. Also drop a line from F perpendicular to BC, meeting BC at H.
2. Let's call the length of BC = a, AC = b, and AB = c. Let's call the height AG = h, and the height of the small triangle (FEC) FH = x.
3. Notice that the two triangles FEC and ABC share the same angle { You can calculate the areas of triangles EDB and DFA by the same method. Then what?
Got it?