Răspuns:
14. a=21,b=9,c=30
15. x=25
16. problema are 3 solutii
17.x∈{1,2,3,4,5,6,7,8,9,10,11,12,13,14}
y∈{14,13,12,11,10,9,8,7,6,5,4,3,2,1}
18.
Explicație pas cu pas:
14. a+b=30 => b=30-a
b+c=39=>c=39-b=39-(30-a)=9+a
c+a=51=> 9 +a+ a=51
2a+9=51
2a=42
a=21
b=30-a=30-21=9
c=9+a=9+21=30
Verificare: a+b=21+9=30
b+c=9+30=39
c+a=30+21=51
15. 2+4+6+...+48+x=1+3+5+7+...+49
2(1+2+3+...+24)+x= 1+3+5+7+...+ (2 . 25-1)
2 . [tex]\frac{24 . 25}{2}[/tex]+ x= 25 . 25
24 . 25+ x= 625
x=625-600
x=25
16.1+2+3+4+5+6=21
6+7+8=21
10+11=21
17.x+y=15
1+14=15, 2+13=15, 3+12=15, 4+11=15, 5+10=15, 6+9=15, 7+8=15, 8+7=15, 9+6=15, 10+5=15, 11+4=15, 12+3=15, 13+2=15, 14+1=15
x∈{1,2,3,4,5,6,7,8,9,10,11,12,13,14}
y∈{14,13,12,11,10,9,8,7,6,5,4,3,2,1}
