1) log3(7-x) = log3(49)
ОДЗ: 7-x > 0 => x < 7
7 - x = 49
x = -42
2) (1/16)^(5-2x) = 2
2^(-4(5-2x)) = 2^1
8x - 20 = 1
8x = 21
x = 21/8 = 2 5/8
3) √(54 + 3x) = x
ОДЗ: x≥0 и x≥-54/3 = -18 => x≥0
54 + 3x - x² = 0
x² - 3x - 54 = 0
D = 9 + 216 = 225
√D = 15
x1 = (3-15)/2 = -6 - не удовлетворяет ОДЗ
x = (3+15)/2 = 9
Ответ: 9