L 10 LGI 60AA 2I I R0 A B2 LG LGI I R ...
Câu 38. L 10 lgI 60
A
A
2
I I r0
A
B
2 lg lg B
B
A
L 10 lg 40B
I0
r 10r 1B
A
r 2rr r 4rM
M
A
32
L L 10 lg r 20 lg 4 M
A
M
rL 47, 96dBChọn B.