F6 Maths 197

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2011-12-13 19:51:43 補充：
a, b是比例常數

2011-12-14 08:27:34 補充：
Area of ABC : Area of BDE = 5 : 2
Area of BDE : Area of ABC = 2 : 5

consider triangle ABE with base AB
triangle ADE : triangle BDE = 1 : 2 (both triangle have a same height from E to base AB)

consider triangle ABC with base AC
triangle ABE : triangle CBE = 3 : 2 (both triangle have a same height from B to base AC)

if area ADE = k => area BDE = 2k
area ABE = area ADE + area BDE = 3k
=> area CBE = 2k => area ABC = k + 2k + 3k = 6k

area BDE : area ABC = 2k : 6k => 1 : 3

2011-12-14 01:01:52 補充：
if area ADE = k => area BDE = 2k
area ABE = area ADE + area BDE = 3k
=> area CBE = 2k => area ABC = 2k + 3k = 5k

area BDE : area ABC = 2k : 5k = 2 : 5

2011-12-14 12:42:34 補充：
area of triangle = 1/2 x base x height
if height is same for both triangle,
=> ratio of area is equivalent to the ratio of base

(don't mix up it with ratio of "SIMILAR" triangle, here is talking about triangles are not similar)