Answer:
expanded:
y = sin(4x)*sin(4x)*cos(3x)
need to use the product rule and chain rule
look at individual derivatives, use chain rule
d/dx sin(4x) = 4cos(4x)
d/dx cos(3x) = -3sin(3x)
put it together using product rule
dy/dx = 4cos(4x)*sin(4x)*cos(3x) + 4cos(4x)*sin(4x)*cos(3x) - 3sin(3x)*sin(4x)*sin(4x)
simplify
dy/dx = 8cos(4x)*sin(4x)*cos(3x) - 3sin(3x)*sin2(4x)
answer is A.
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