The correct answer is seven. The first white square is placed on the top of the blue square, so the sides of it will make 45 degree angle and the intersection of the two squares is an octagon.
We place two squares on opposite sides of the white square, so we form a band of three square that will cover central part of the square.
Each of the remaining two angles can be covered by two squares. 2 + 3 + 2 = 7.
Any questions?

Sava D.
08/16/20
Many J.
Is there a way to express this mathematically?08/16/20

Sava D.
08/16/20

Sava D.
08/16/20
Nikhil S.
I also concluded 7, but I still haven't been able to prove that eight is not possible. Do you have a proof of this or an idea for one?08/17/20

Sava D.
08/17/20
Many J.
Wouldn’t it be 5 squares? 1+2+2?08/16/20