by about how much will

g(x,y,z)=x+x*cosz-y*sinz+y

change if the point p(x,y,z) moves from p(initial)=(2,-1,0) a distance of ds=0.2units towards the point p(final)=(0,1,2)

i know we have to find df here

directional derivative=df/ds

but how to use above information to establish the result