Answer:
13) Angle A is 30°
14) Angle A is 45°
15) Angle A is 40°
16) Angle A is 40.5°
Explanation:
By the angle sum theorem for the interior angles of a triangle, we have;
13) 130° + 2·x + 3·x = 180°
∴ 2·x + 3·x = 180° - 130° = 50°
2·x + 3·x = 5·x = 50°
x = 50°/5 = 10°
∠A = 3·x = 3 × 10° = 30°
∠A = 30°
14) 3·x + 9 + 4·x + 9 + 78° = 180°
7·x + 18 + 78° = 180°
7·x = 180° - (18 + 78)° = 180° - 96° = 84°
x = 84°/7 = 12°
∠A = 3·x + 9 = 3 × 12° + 9 = 45°
∠A = 45°
15) 90° + x + 51 + x + 61 = 180°
∴ x + 51 + x + 61 = 180° - 90° = 90°
2·x + 112 = 90°
2·x = (90 - 112)° = -22°
x = -22°/2 = -11°
x = -11°
∠A = x + 51 = -11° + 51 = 40°
∠A = 40°
16) x + 79 + x + 49 + 70° = 180°
x + x = (180 - 70 - 79 - 48)° = -17°
2·x = -17°
x = -17°/2 = -8.5°
x = -8.5°
∠A = x + 49 = (-8.5 + 49)° = 40.5°
∠A = 40.5°.