Deriving the partial chain rule using first principles

Question

Can someone derive the chain rule for ∂/∂x(T) using first principle where T is a function of x(r,θ,φ),y(r,θ,φ),z(r,θ,φ) ?

The equation goes like:

∂T/∂x=∂T/∂r(∂r/∂x)+∂T/∂θ(∂θ/∂x)+∂T/∂φ(∂φ/∂x)

How can you prove it from first principle?