1) 23-47+29-33+8= -20
2)7,42-2,12+8,38-7,78+0,9=6,8
3) 4 5/7+2 3/14-6 5/9-2 4/9+6 11/14=4 5/7
4)1,85-1 5/6-2 1/6-2,85+6,75=1,75
3 = lg(1000)
lg(1000) - lg(x-27) = lg(1000/(x - 27))
lg(3x -11) = lg(1000/(x - 27))
3x - 11 = 1000/(x -27)
(3x - 11)*(x -27) - 1000 = 0
3x^2-92x-703 = 0
x = 37, x = -19\3
ОДЗ:
x - 27 > 0
x - 27 != 1
3x - 11 >0
x > 27,
x != 28
x > 11\3
x > 27 и x != 28
C учетом ОДЗ ответ: x = 37;
1.9*10 равно 90
2.90/2 равно 45
3.90+45 равно 135