Step-by-step explanation:
step 1. the 3 internal angles of a triangle add up to 180°. let x be the 3rd angle
step 2. x + 34 + 72 = 180
step 3. x = 74°.
step 4. for problem 5 let the internal angles be a, b, and c
step 5. so b = 2a - 10, c = b + 25
step 6. we also know that a + b + c = 180
step 7. so a + (2a - 10) + (b + 25) = 180 by substitution
step 8. a + (2a - 10) + ((2a - 10) + 25) = 180 also by substitution
step 9. 3a - 10 + 2a + 15 = 180
step 10. 5a + 5 = 180
step 11. a = 35°
step 12. therefore b = 2a - 10 = 60°, c = 85°.
