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Alfie
Bovine Member

 Posted: Thu Oct 19, 2000 4:44 am    Post subject: 1 I am putting this here because it belongeth not to any other place. f(x)=cos(-xi)+sin(-xi)i Find the first derivitive of f(x). What does this mean and why would I find it interesting?
Ghost Post
Icarian Member

 Posted: Thu Oct 19, 2000 1:18 pm    Post subject: 2 Please correct me if I'm wrong... e^iz = cos(z) + i*sin(z) let z = -ix so... f(x) = e^(i*(-ix)) i^2 = -1 f(x) = e^x therefore f'(x) = e^x The derivitate is the same as the function. [This message has been edited by Matt (edited 10-19-2000).]
CrystyB
Misunderstood Guy

 Posted: Sat Nov 18, 2000 5:22 pm    Post subject: 3 I'll have to make a note of this in me "Dearest and Beloved Problems"! My answer would have been (at any hour of the day, after no-matter-how-many math experiences for the day): [cos(alpha(x))]'=[-sin(alpha(x))]*[alpha'(x)] and [sin(alpha(x))]'=[cos(alpha(x))]*[alpha'(x)] so f'(x)=i*sin(-ix)+i*(-i)*cos(-ix)=cos(ix)-i*sin(ix). And just now my experiences for the day would make a difference: i wonder how soon would i have noticed that f'=f so f=ct*e^x... edited on 11-18-2000 and [This message has been edited by CrystyB (edited 11-30-2000).]
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