mean value theorem- gradient

Hi please , can someone help me with this problem.
I need to know the procedure.

Let f(x,y)=x^3-xy. set a(0,1) and b(1,3).
Find a point c on the line sement[ab] for which

f-f[a]= gradient(f[c]) * (b-a)

Thank you

Braddy

 

wats gradient ? does it mean f '[c]