I explain step by step how to find the inf sup max and min functions in 2 variables??
Then I write four paragraphs that are able to solve
arctan (x ^ 4 + y ^ 4)
arctan (x ^ 3 + y ^ 4)
ln (x ^ 4 + y ^ 4)
2x + arctan (x ^ 3)
arctan (sin (x + y))
THANKS MILLEEEE