There are 4 days in the Sunday

Tomorrow is April 30th. Yesterday was April 28th 

Last week it was 5th on Sunday

We have:

a3+b3=(a+b)(a2+ab+b2)=2a3+b3=(a+b)(a2+ab+b2)=2 (*)

Other way:

a2+ab+b2=a2+2.12b+(12b)2+34b2a2+ab+b2=a2+2.12b+(12b)2+34b2

=(a+12b)2+34b2=(a+12b)2+34b2

Because (a+12b)2≥0(a+12b)2≥0 with ∀a,b∀a,b

34b2≥034b2≥0 with ∀b∀b

So (a+12b)2+34b2≥0(a+12b)2+34b2≥0 with ∀a,b∀a,b

or a2+ab+b2≥0a2+ab+b2≥0 with ∀a,b∀a,b (**)

From (*) and (**) we have  a+b≤2a+b≤2

Your ex is so hard to do :)