Exercitiul 16:
l-7l = 7
l12l = 12
l4l = 4
l-2l = 2
l-25l = 25
l17l = 17
l0l = 0
l-10l = 10
l-15l = 15
Exercitiul 17:
a) l-10l > -10
10 > -10 (adevarat)
b) l2l = 2
2 = 2 (adevarat)
c) l-3l = -3
3 = -3 (fals)
d) l-4l < 2
4 < 2 (fals)
e) l2l = 1
2 = 1 (fals)
Exercitiul 18:
a) l-1l + l-2l + l-3l + ..... + l-10l = 1 + 2 + 3 + ..... + 10 = (10 + 1) x 10 : 2
= 11 x 5 = 55
b) l-1l + l2l + l-3l + ..... + l10l = 1 + 2 + 3 + .... + 10 = 55
c) l-9l + l-7l + l-5l + l-3l + l-1l + l1l + l3l + l5l + l7l + l9l = 9 + 7 + 5 + 3 + 1 + 1 + 3 + 5 + 7 + 9 = 2 x 9 + 2 x 7 + 2 x 5 + 2 x 3 + 2 x 1 = 2(1 + 3 + 5 + 7 + 9) = 2 x 25 = 50
