1) 3^(x+1) +3^(x+2) +3^(x+3) +3^(x+4)=120
3^x(3^1 +3^2 +3^3 +3^4)=120
3^x(3+9 +27 +81)=120
3^x120=120
3^x=1
x=0
2)(2 la puterea 2x+1 ori 3 la puterea x + 4 la puterea x ori 3 la puterea x+2):12 la puterea x=n
[2^(2x+1)× 3^x + 4^x × 3^(x+2)]:2^2x ×3^x=n
(2^2x ×2× 3^x + 2^2x × 3^x+3^2):2^2x ×3^x=n
(2^2x ×2× 3^x + 2^2x × 3^x ×3^2):2^2x ×3^x=n
2+3^2=n
n=2+9=11
3) a-b=725 si a:b=37 rest 5 aflati a,b
a=37b+5
37b+5-b=725
36b=720
b=20
a=725+20=745
