Răspuns:
9. 1,19
10. 8
11.650
12.a=5
b=7
c=9
13.a=26,b=8
a=8,b=26
Explicație pas cu pas:
9. 1,2²-0,5²=1,44-0,25=1,19
10.b+c=2
1+1=2
a=2
b=1
c=1
(2²)¹ × (2¹)¹
4¹×2¹
4×2=8
11. 2+4+.......+50
N=(50-2):2+1
N=48:2+1
N=24+1
N=25
S=(50+2)×25:2
S=52×25:2
S=26×25
S=650
12. (a+b+c):3=7
b=a+1
c=a+2
(a+b+c):3=7/×3
a+b+c=21
a+a+1+a+2=21
3a=19=>rezulta ca numerele a b c sunt consecutive pare
b=a+2
c=a+4
a+b+c=21
a+a+2+a+4=21
3a+6=21
3a=15
a=5
b=a+2
b=5+2
b=7
c=a+4
c=5+4
c=9
13. primul caz
a-b=18=>a=b+18
a:b=3 rest 2=>a=3b+2
3b+2=b+18/-2
3b=b+16/-b
2b=16
b=8
a=b+18
a=8+18
a=26
al doilea caz
b:a=3 rest 2=>b=3a+2
b-a=18=>b=a+18
3a+2=a+18/-2
3a=a+16/-a
2a=16/:2
a=8
b=a+18
b=8+18
b=26
