D =(-8)² - 4·1·(-9) = 64 + 36 = 100
x1 = (8 - √100)/2·1 = -1 не подходит (x-8>0; x> 8)
x2 = (8 + √100)/2·1 = 9
заменим 2 на 2 = log3 9
log3 (x*(x-8)) = log3 9
x*(x-8) = 9
x² -8x -9 = 0
D =(-8)² - 4·1·(-9) = 64 + 36 = 100
x1 = (8 - √100)/2·1 = -1 не подходит (x-8>0; x> 8)
x2 = (8 + √100)/2·1 = 9
2) log2(x-7)<3
3 = log2 8
log2(x-7)< log2 8
x-7< 8
x< 8+7
x<15
x-7>0
x>7
x∈ (7; 15)