Four waves are described by the following expressions, where distances are measured in meters and times in seconds
I y = 0.12 cos(3x - 21t)
II y = 0.15 sin(6x + 42t)
III y = 0.13 cos(6x + 21t)
IV y = -0.23 sin(3x - 42t)
Which of these waves travel in the +x direction?
A)
I and II
B)
I and III
C)
II and IV
D)
I and IV
E)
II and III
D
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