# Formulas Explained

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Videos to explain Standard Deviation Formula, Fibonacci Formula, Completing the square and Quadratic Formula.

Standard Deviation Formula Explained
The formula for standard deviation looks scary and feels scary. Why on earth would anyone want to measure a sense of "spread" of data values with a formula like that??!!!? Well, let me tell you the very natural and very human story that explains why.
Fibonacci Formula
The Fibonacci numbers begin 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, .... What's the 100th number in this list? The 587th number? In this video we derive a general formula the N-th Fibonacci number.
(WARNING: This video assumes complete familiarity with solving a quadratic equation, basic properties of exponents, and solving a tiny system of equations.)

Completing the Square Part I
Here's the simple way to solve quadratic equations by completing the square.
Completing the Square Part II
Here's the second section of video on how to solve quadratics with ease.

After learning how to complete the square, see how quickly and magically the famous quadratic formula pops out at you!

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You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.