Math Is Fun Forum

Zeeshan 01

Member

Registered: 2016-07-22

Posts: 746

Derivative

F(x)=e^x * cos (x-a)
Want to exercise this type of question
Know simple derivation but want to get this answer that is
Derivative=re^x cos(x-a+thetha)
R=sqrt 2 thetha=pi/4

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Malik

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Derivative

hi Zeeshan 01

There are two stages to this problem.  I think you have done the first but I'll say anyway.

This is a product of two functions so use the product rule:

You can combine the trig functions into a single trig function using the compound angle formulas.  You want a cosine so I'll use

To make the derivative look like the right hand side here:

Hope that helps,

Bob

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Children are not defined by school ...........The Fonz
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Sometimes I deliberately make mistakes, just to test you!  …………….Bob