a, 2.3\(x+1\) + 38 = 23.52
2.3\(^{x+1}\) + 38 = 200
2.3\(^{x+1}\) = 200 - 38
2.3\(^{x+1}\) = 162
3\(^{x+1}\) = 162 : 2
3\(^{x+1}\) = 81
3\(^{x+1}\) = 34
\(x+1\) = 4
\(x\) = 3
b, 2\(^{x+1}\) + 4.2\(^x\) = 3.25
2\(^x\).(2 + 4) = 96
2\(^x\).6 = 96
2\(^x\) = 96 : 6
2\(^x\) = 16
2\(^x\) = 24
\(x\) = 4
d) (2x + 15) + 18 = 55 : 53
(2x + 15) + 18 = 52
(2x + 15) + 18 = 25
2x + 15 = 25 - 18
2x + 15 = 7
2x = 7 - 15
2x = -8
x = -8 : 2
x = -4
c;
\(x\) \(\in\) BC(12; 15; 40)
12 = 22.3; 15 = 3.5; 40 = 23.5
BCNN(12; 15; 40) = 23.3.5 120
\(x\in\) BC(120) = {0; 120; 240; 360; 480;..;}
Vì 350 < \(x\) < 400
Nên \(x\) = 360