Отрицательная степень означает деление.
1) (1/2)^(5x-9) = 1*2⁹ / 2^(5x)
1*2⁹ / 2^(5x) = 1/2⁶
Отсюда получаем 2^(5x) = 2^(9+6)
2^(5x) = 2¹⁵
5x = 15 x = 3
2) (1/2)^(6-2x) = 2²
1*2^(2x) / 2⁶ = 2²
2^(2x) = 2⁶ * 2²
2^(2x) = 2⁸
2x = 8 x = 4
3) (1/7)^(5x-3) = 1/7²
7³ / 7^(5x) = 1 / 7²
7^(5x) = 7⁵
5x = 5 x = 1
4) (1/3)^(8-3x) = 3⁴
3^(3x) = 3¹²
3x = 12 x = 4