(1) g((x1+x2)/2)=(x1+x2)^2/4 + a(x1+x2)/2 +b
(2) (g(x1)+g(x2))/2=(x1^2+x2^2+a(x1+x2))/2 +b
(2)-(1):
(x1^2+x2^2)/4 - (x1x2)/2
=(x1^2-2x1x2+x2^2)/4
=(x1-x2)^2 /4
>=0
证毕
(1) g((x1+x2)/2)=(x1+x2)^2/4 + a(x1+x2)/2 +b
(2) (g(x1)+g(x2))/2=(x1^2+x2^2+a(x1+x2))/2 +b
(2)-(1):
(x1^2+x2^2)/4 - (x1x2)/2
=(x1^2-2x1x2+x2^2)/4
=(x1-x2)^2 /4
>=0
证毕