In triangle ABC, de ∥ BC ad: DB = 2:1, if the area of trapezoidal dbec is 10cm, the area of triangle ABC can be obtained

∵DE∥BC,∴ΔADE∽ΔABC,
∴DE/BC=AD/AB=2/3,
∴SΔADE/SΔABC=4/9,
∴SΔADE/(SΔADE+10)=4/9,
9SΔADE=4SΔADE+40
SΔADE=8.

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