4 * 2^{2x} - 6^x = 18 * 3^{2x}
4 * 2^{2x} - (2*3)^x = 18 * 3^{2x}
4 * (2^x)^2 - 2^x * 3^x = 18 * (3^x)^2
Разделим обе части на (3^x)^2
4 * (2^x / 3^x)^2 - (2^x / 3^x) = 18
Пусть y = (2/3)^x.
4y^2 - y = 18
4y^2 - y - 18 = 0
D = (-1)^2 - 4 * 4 * (-18) = 1 + 288 = 289
y_1 = (1 + √289) / (2 * 4) = (1 + 17) / 8 = 18 / 8 = 9/4
y_2 = (1 - √289) / (2 * 4) = (1 - 17) / 8 = -16 / 8 = -2
Вернёмся к замене:
(2/3)^x = 9/4
(2/3)^x = (3/2)^2 = (2/3)^{-2}
x = -2
(2/3)^x = -2
Нет решений
Ответ: x = -2