{1/(4πt)^(n/2)}'=-n/{2^(n+1)*t(πt)^(n/2)}、{e^(-|x-y|^2/4t)}'=e^(-|x-y|^2/4t)*{|x-y|^2/(4t^2)} から、
-n/{2^(n+1)*t(πt)^(n/2)}*e^(-|x-y|^2/4t) + e^(-|x-y|^2/4t)*{|x-y|^2/(4t^2)}*{1/(4πt)^(n/2)}
=e^(-|x-y|^2/4t)*{-n/{2^(n+1)*t(πt)^(n/2)}+{|x-y|^2/(4t^2)}*{1/(4πt)^(n/2)}}
=(|x-y|^2-2nt)*e^(-|x-y|^2/4t)/{(4t^2)*(4πt)^(n/2)}