THANKS A LOT. I DID IT IN THIS WAY, BUT I DID NOT USE THE CONDITION LIKE a(p) and b(p) are linear homo and concave, do you know why? thank you very much.
Could I ask you another question as follows:
" Even though some goods may be inferior, it must be true that at least one good is nomal regardless of tastes"
Is it true or not? Could you give me some hint?
I really appreciate it.