Rename mixed numbers before you can subtract are what

In triangle abc segment de is parallel to the side ac . (the endpoints of segment de lie on the sides ab and bc respectively). find de, if ac=20cm, ab=17cm, and bd=11.9cm;

Triangle inequality theorem state if each set of three numbers can be the lengths of the sides of a triangle. 1. 9, 8, 22. 2. 5,10,12. 3. 7,10,22. 4. 4,11,12. 5. 11,9,10. 6. 10,4,19. 7. 3,12,10. 8. 4,3,2. 9. 6,5,13. 10. 7,12,20. me .

Given that sin∅ = 1/4, 0 < ∅ < π/2, what is the exact value of cos∅? a. (√4)/4 b. (√15)/4 c. (4π)/2 d. (4√2)/4