27. connection AC s =1/2 * (15 * 36-12 * 9) = 216.
28.a^2+b^2=c^2
The second, third and fourth photos
12. right angle b
13. 108
14.2: 1
17. 12/5
18. Right angle
19.2
20. 17
2 1.5^2+ 12^2= 13^2
22.36 connecting BD
(All are done by hand on site, please adopt)
23.a=24 b= 18 c=30 right triangle
24. 120