(The one circled in black) , i understood that we should look now over the region of x and y since we had the result of the 2nd partial derivative polynomial however i didn't know how they considered x is positive and how e^y became less than or equal to e^0.2

20 bed the lineofization of fayebet at ( 1jo ), Then And an upper bound of the effor in the approximachen 1 41 2 0 .2 ( 10 ) f xy = 3 x 2 ey fly= x ey