diff --git a/SICP/exercise_1_40.janet b/SICP/exercise_1_40.janet
new file mode 100644
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--- /dev/null
+++ b/SICP/exercise_1_40.janet
@@ -0,0 +1,29 @@
+(def tolerance 0.00001)
+(defn fixed-point [f first-guess]
+  (defn close-enough? [v1 v2]
+    (< (math/abs (- v1 v2))
+       tolerance))
+  (defn try-it [guess]
+    (let [next (* 0.5 (+ guess (f guess)))]
+      (if (close-enough? guess next)
+        next
+        (try-it next))))
+  (try-it first-guess))
+
+(def dx 0.00001)
+(defn deriv [g]
+  (fn [x] (/ (- (g (+ x dx)) (g x)) dx))) 
+
+(defn newton-transform [g]
+  (fn [x] (- x (/ (g x) ((deriv g) x)))))
+(defn newtons-method [g guess]
+  (fixed-point (newton-transform g) guess))
+
+(defn cubic [a b c]
+  (fn [x]
+    (let [cub (* x x x)
+          qua (* a x x)
+          sing (* b x)]
+      (+ cub qua sing c))))
+
+(print (newtons-method (cubic 5 3 -1) -10))
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