Answer:
ΔABC
∠9 = ∠19 + ∠21
∠7 = ∠20 + ∠21
∠8 = ∠19 + ∠20
ΔXYZ
∠3 = ∠11 + ∠12
∠5 = ∠10 + ∠12
∠4 = ∠10 + ∠11
ΔNOR
∠1 = ∠5 + ∠6
∠2 = ∠ 4 + ∠5
∠3 = ∠4 + ∠6
Explanation:
According to the exterior angle theorem, the exterior angle of a triangle is equal in measurement to the sum of the two interior angles of the triangle;
In triangle ΔABC, we have;
∠9 = ∠19 + ∠21
∠7 = ∠20 + ∠21
∠8 = ∠19 + ∠20
In triangle ΔXYZ, we have;
∠3 = ∠11 + ∠12
∠5 = ∠10 + ∠12
∠4 = ∠10 + ∠11
In triangle ΔNOR, we have;
∠1 = ∠5 + ∠6
∠2 = ∠ 4 + ∠5
∠3 = ∠4 + ∠6