Find the derivative of the vector function

[xstetsonx]

Find the derivative of the vector function r(t) = ta x (b + tc)
a=<-2,2,-1> b=<-1,1,1> c=<-2,2,4>


I know r(t)=ta x (b + tc)=(axb)t+(axc)t^2
then i got lost

 

[tiny-tim]

Hi xstetsonx!

(try using the X² tag just above the Reply box )

I know r(t)=ta x (b + tc)=(axb)t+(axc)t^2

ok, now differentiate wrt t.

 

[xstetsonx]

don't know how because they are all numbers. Should i do the cross product or what do i do?

 

[tiny-tim]

uhh? everything except t is a constant

 

[HallsofIvy]

Everything except t is a constant vector. t is the only numeric variable in the problem.