Add all the A tasks

Task/Arithmetic-geometric-mean/Python/arithmetic-geometric-mean-1.py

@@ -0,0 +1,16 @@
+from math import sqrt
+
+def agm(a0, g0, tolerance=1e-10):
+    """
+    Calculating the arithmetic-geometric mean of two numbers a0, g0.
+
+    tolerance     the tolerance for the converged
+                  value of the arithmetic-geometric mean
+                  (default value = 1e-10)
+    """
+    [an, gn] = [(a0 + g0) / 2.0, sqrt(a0 * g0)]
+    while abs(an - gn) > tolerance:
+        [an, gn] = [(an + gn) / 2.0, sqrt(an * gn)]
+    return an
+
+print agm(1, 1 / sqrt(2))

Task/Arithmetic-geometric-mean/Python/arithmetic-geometric-mean-2.py

@@ -0,0 +1,10 @@
+from decimal import Decimal, getcontext
+
+def agm(a, g, tolerance=Decimal("1e-65")):
+    while True:
+        a, g = ((a + g) / 2, (a * g).sqrt())
+        if abs(a - g) < tolerance:
+            return a
+
+getcontext().prec = 70
+print agm(Decimal(1), 1 / Decimal(2).sqrt())