1.∵AN = x ∴AM = x/3 × 4 = 4x/3
∴S = AN × AM = 4x^2/3
∵S < 64
∴4x^2/3 < 64
∴定义域:-4√3 < x < 4√3
2.AN = 3时,矩形AMPN的面积最小
最小面积为12