Answer:
Step-by-step explanation:
Area of a trapezium is the average of the parallel sides times the distance between them.
If we subtract 15 units from each of the parallel sides, we end up with a triangle that has two sides of 8 units and one of 10 units. One of the 8 unit sides is the base and we need to find the height h which is perpendicular to this base.
Let the base be split into two segments, call one A, the other will be 8 - A
From Pythagoras.
10² - A² = h² = 8² - (8 - A)²
10² - A² = 8² - (8 - A)²
100 - A² = 64 - (64 - 16A + A²)
100 - A² = 64 - 64 + 16A - A²
100 = 16A
A = 6.25
h = √(10² - 6.25²)
h = √60.9375
A = ½(15 + 23)√60.9375
A = 148.31870246... ≈ 148.3 cm²
