Write a Riemann sum to estimate $A(g, 0 ≤ x ≤ 2)$ for $g(x) = -x^2 + 4$ using $n$ left endpoint rectangles.

1. Then calculate for $n = 20$.

   Hint (a):

   Substitute.

2. How can you use your result to estimate $A(g, -2 ≤ x ≤ 0)$? $A(g, -2 ≤ x ≤ 2)$?

   Hint (b):

   Consider the shape of the graph of $g(x)$.