tentukan nilai dari f' 0
f'(0) = -3
pembahasan :
f(x) = -3xcos(3x)
u = -3x
u' = -3
v = cos(3x)
v' = 3(-sin(3x))
f'(x) = u'v + uv'
= -3cos(3x) + -3x(3(-sin(3x))
= -3cos(3x) + 9xsin(3x)
f'(0) = -3cos(3x) + 9xsin(3x)
= -3cos(3(0)) + 9(0)sin(3(0))
= -3cos0 + 0
= -3(1)
= -3
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