added fibonacci using formula along with test cases

Maths/FibonacciUsingFormula.js

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+// https://en.wikipedia.org/wiki/Fibonacci_sequence
+
+/*
+    Nth Fibonacci Number :
+        Fn = (((1+sqrt(5))^n) - ((1-sqrt(5))^n))/(2^n)*sqrt(5)
+    
+    Complexities : 
+        TC - O(1)
+        SC - O(1)
+*/
+const FibonacciUsingFormula = (n) => {
+    const sqrt5 = Math.sqrt(5);
+    const phi = (1 + sqrt5) / 2;
+    const psi = (1 - sqrt5) / 2;
+    const result = (Math.pow(phi, n) - Math.pow(psi, n)) / sqrt5;
+    return Math.round(result);
+}
+
+export { FibonacciUsingFormula };

Maths/test/FibonacciUsingFormula.test.js

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+import { FibonacciUsingFormula } from '../FibonacciUsingFormula'
+
+describe('FibonacciUsingFormula' , () => {
+    it('should calculate the correct Fibonacci number for n = 0', () => {
+        const result = FibonacciUsingFormula(0)
+        expect(result).toBe(0)
+    })
+    it('should calculate the correct Fibonacci number for n = 1', () => {
+        const result = FibonacciUsingFormula(1)
+        expect(result).toBe(1)
+    })
+    it('should calculate the correct Fibonacci number for n = 2', () => {
+        const result = FibonacciUsingFormula(2)
+        expect(result).toBe(1)
+    })
+    it('should calculate the correct Fibonacci number for n = 5', () => {
+        const result = FibonacciUsingFormula(5)
+        expect(result).toBe(5)
+    })
+    it('should calculate the correct Fibonacci number for n = 10', () => {
+        const result = FibonacciUsingFormula(10)
+        expect(result).toBe(55)
+    })
+    it('should calculate the correct Fibonacci number for n = 15', () => {
+        const result = FibonacciUsingFormula(15)
+        expect(result).toBe(610)
+    })
+})