diff --git a/numpy_questions.py b/numpy_questions.py
index 07a10c1..0f3d5c9 100644
--- a/numpy_questions.py
+++ b/numpy_questions.py
@@ -40,7 +40,13 @@ def max_index(X):
     i = 0
     j = 0
 
-    # TODO
+    if not isinstance(X, np.ndarray):
+        raise ValueError("Input must be a numpy array.")
+
+    if X.ndim != 2:
+        raise ValueError("Input array must be 2D.")
+
+    i, j = np.unravel_index(np.argmax(X), X.shape)
 
     return i, j
 
@@ -64,4 +70,12 @@ def wallis_product(n_terms):
     """
     # XXX : The n_terms is an int that corresponds to the number of
     # terms in the product. For example 10000.
-    return 0.
+    if n_terms < 0:
+        raise ValueError("Number of terms must be non-negative.")
+
+    product = 2.0
+
+    for i in range(1, n_terms + 1):
+        product *= (4 * i ** 2) / (4 * i ** 2 - 1)
+
+    return product