Acute angles because they are less then 90 degrees which is a right angle.
Let the side length of the square be x, then A = x^2
but diagonal (z) = sqrt(2x^2)
z^2 = 2x^2
x^2 = 1/2 z^2
Thus, A = 1/2 z^2
dA/dz = 1/2 (2z) = z
The rate of change is z.
When z = 4, the rate is 4.
-2(2x-1)(x+3) = ((-2)2x - (-2)(-1))(x+3) = (-4x-2)(x+3)