Răspuns:
Explicație pas cu pas:
11.
a) 11 + 17 = 28
A_________B____________C
b) 5 + 13 = 18
C __________A_____B
c) 6 + 15 = 21
A_____C____________B
12.
A_ _ _ _ _ _ _ _ _ _ _ _B_ _ _ _ _ _ _C
BC = AC - AB = 19 - 12 = 7 cm
14.
A_______C_______B_______D
BC = 3 cm
BC = BD
AC = CB
AD = AC + BC + BD = 3 + 3 + 3 = 9 cm