已知实数a,b满足a+b=1,则b=1-a
a^2+b^2
=a^2+(1-a)^2
=2a^2-2a+1
=2(a-1/2)^2+1/2
≥1/2
当且仅当a=b=1/2时取到最小值1/2.
则代数式a^2+b^2最小值是1/2