diff --git a/ps16-3.py b/ps16-3.py
index ca44b44..6c0c60b 100644
--- a/ps16-3.py
+++ b/ps16-3.py
@@ -28,7 +28,10 @@ def cot(x):
 def func(z: float) -> float:
     first = np.sqrt((z0 / z) ** 2 - 1)
     second = cot(z)
-    return first - second
+    return first + second
 
 
-print(find_root(func, 6.2, 6.4, max_iter=1000))
+print(find_root(func, 0.1, 3, max_iter=1000))
+print(find_root(func, 3.1, 6, max_iter=1000))
+print(find_root(func, 6.1, 8, max_iter=1000))
+print(find_root(func, 10, 12, max_iter=1000))