2ˣ⁺¹+2ˣ⁻¹+2ˣ=28,
2ˣ·2¹+2ˣ:2¹+2ˣ=28,
2ˣ·2+2ˣ·2⁻¹+2ˣ=28,
2·2ˣ+2⁻¹·2ˣ+2ˣ=28,
3·2ˣ+½·2ˣ=28,
(3+½)·2ˣ=28,
3,5·2ˣ=28,
2ˣ=2·4,
2ˣ=8,
2ˣ=2³,
х=3.
ответ: 3.
