Log2 (5x-7) - log2 5=log2 21

Log2 (5 * x - 7) - log2 5 = log2 21;

ОДЗ.

5 * x - 7 > 0;

5 * x > 7;

x > 7/5;

x > 1 2/5;

x > 1.4.

Упростим.

Log2 (5 * x - 7) = log2 5 + log2 21;

Log2 (5 * x - 7) = log2 (5 * 21);

Log2 (5 * x - 7) = log2 105;

5 * x - 7 = 105;

5 * x = 105 + 7;

5 * x = 112;

x = 112/5;

x = 20 + 2 + 0.4;

x = 22.4;

Ответ: х = 22,4.