Let’s build the height BH of the trapezoid ABCD.
Knowing the area of the trapezoid and the length of its bases, we determine the length of the height BH.
Savsd = (ВС + АD) * ВН / 2.
BH = 2 * Sfvsd / (BC + AD) = 2 * 77 / (3 + 8) = 2 * 7 = 14 cm.
Let’s draw the height AK of triangle ABC. The height of the AK of the triangle is equal to the height BH of the trapezoid BACD, since the quadrilateral AKBH is a rectangle. Then AK = BH = 14 cm.
Determine the area of the triangle ABC.
Savs = BC * AK / 2 = 3 * 14/2 = 21 cm2.
Answer: The area of triangle ABC is 21 cm2.
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