⊆ = Subset
∈ = Element
Definition:
If all the elements of a set is contained in ANOTHER set, then the set whose elements are contained in another set is a subset.
Ex. Set A 's elements= 1,2,3 Set B's elements= 1,2,3,4,5 so... that means all the elements of Set A are in Set B, so A ⊆ B.
Prove that for any two numbers x,y we have [(x^2 + y^2)/2] >= x + y - 1
Solution)
For any number a we have have a^2 > 0. So,
(x-1)^2 + (y-1)^2 >= 0
And if we solve this we get the solution.I don't get the red part.