Zara F.

asked • 12/05/23

Understanding Derivatives

y = cos4(7x3)

step 1 dy/dx = 4cos3(7x3)(-sin(7x3))*21x2

step 2 = -84x2cos3(7x3)sin(7x3)

step 3 = -42x2sin(14x3)cos2(7x3)


Could someone explain how they went from step 2 to step 3?


Edit: I understand it now! (2sinxcosx = sin2x)

Inactive Tutor

That's right: the addition formula is sin (x+x) = (sin x)(cos x) + (cos x)(sin x) Therefore sin (2x) = 2(sin x)(cos x)
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12/05/23

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