Question #a8f2b

1 Answer
Øko
Feb 5, 2018

#dy/dx=-5sin(5x)#

Explanation:

We want to differentiate

#y=cos(5x)#

Use the chain rule #dy/dx=dy/(du)*(du)/dx#

Let #y=cos(u)# and #u=5x#

Then #dy/(du)=-sin(u)# and #(du)/dx=5#

Therefore by the chain rule

#dy/dx=-sin(u)*5#

Substitute #u=5x#

#dy/dx=-5sin(5x)#

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