Find the total differential for

Question

f(x,y,z)= cos(4x+3y+2z+1)

Answer 1

df = df/dx dx + df/dy dy + df/dz dz
let R = 4x+3y+2z+1
= -4sin(R)dx -3 sin(R) dy -2 sin(R)dz

= -sin(4x+3y+2z+1)(4 dx + 3 dy + 2 dz)