Question

In the figure to the right, ABCD is rectangle. Find the area of △ABC, if the area of △AOD is 10.

Answer 1

The correct answer is: Area of △ABC = 20

Explanation:
Since the area of △AOD = 10; therefore. the area of △BOC is also 10.

Now:
The area of △ABC = Area of △AOB + Area of △BOC --- (1)

Since Area of △AOB = $\frac{1}{2}$ (Area of △ABC) --- (2)

Plug (2) in (1):
(1) => Area of △ABC = $\frac{1}{2}$ (Area of △ABC) + 10
=> $\frac{1}{2}$ (Area of △ABC) = 10
=> (Area of △ABC) = 20

-i