F.4 數學(面積) (10分)

Let area of triangle OAB=x
Let area of triangle BOC=y
Let area of triangle COD=z
Let area of triangle DOA=m.
Therefore, we get the following set of equations:
x + y = 5 (1)
y + z = 9 (2)
z + m = 10 (3) and
m + x = 6 (4)
However, there is no unique solution to this set of equation, x can be any value between 0 (because area cannot be negative) and 5 (because y cannot be negative).

△ABC,△BCD,△CDA,△DAB加埋所形成的面積是兩個四邊形ABCD的面積
所以四邊形ABCD的面積=(5+9+10+6)/2
=15
△OAB的面積=1/4*ABCD的面積
=15/4