Find a vector w with the same direction of u but twice as long as v. u = {0 4 2} v = {2 1 0}.

Find magnitude of v and then double itFind unit vector of u Multiply the above two

Let's do it step by step:

Magnitude of v and then double itmagnitude||v||=√2^2+1^2+0^2=√5 double it become  =2√5
Find unit vector of u magnitude||u||=√0^2+4^2+2^2=2√5 
so  unit.vector={0,2/√5,1/√5}

Multiply the above two:

when u multiply u get ( 0, 4/5, 2/5)

From negative to negative