Similarity of triangles
Answers are for parents and teachers.
1
△ABC has ∠A = 80°, ∠B = 40°; △DEF has ∠D = 80°, ∠F = 60°. Are they similar? Which vertices match?
∠C = 60° and ∠E = 40°. Yes (AA): A → D, B → E, C → F.
2
In △ABC, DE ∥ BC with AD = 5, DB = 3, AC = 12 and DE = 10. Find AE and BC.
AB = 8, k = 5/8. AE = 12 × 5/8 = 7.5 and BC = 10 × 8/5 = 16.
3
Are the triangles with sides 7, 9, 12 and 14, 18, 24 similar? Find k.
7 ÷ 14 = 9 ÷ 18 = 12 ÷ 24 = 1/2. Similar (SSS), k = 1/2.
4
In a right triangle the altitude to the hypotenuse cuts it into BD = 4 and DC = 9. Find the altitude AD and the hypotenuse BC.
AD² = 4 × 9 = 36, so AD = 6. BC = 4 + 9 = 13.
5
A 2 m pole has a shadow 1.5 m long. At the same time a tower’s shadow is 36 m. How tall is the tower?
2 ÷ 1.5 = h ÷ 36, so h = 36 × 2 ÷ 1.5 = 48 m.