Răspuns:
[tex]20)a) {3}^{x} + {3}^{x - 1} = 4 \\ {3}^{x} + {3}^{x} \div 3 = 4 | \times 3 \\ 3 \times {3}^{x} + {3}^{x} = 12 \\ 4 \times {3}^{x} = 12 \\ {3}^{x} = 3 \\ x = 1[/tex]
[tex]b)5 \times {3}^{x} - 2 \times {3}^{x} = 81 \\ {3}^{x} \times (5 \times 1 - 2 \times 1) = 81 \\ {3}^{x} \times 3 = 81 \\ {3}^{x} = 81 \div 3 \\ {3 }^{x} = 27 \\ {3}^{x} = {3}^{3} \\ x = 3[/tex]
Acolo e punctul c nu b
