Need help proving the cos(a+b) = (cos a)(cos b)(sin a)(sin b) trigonometric identity? This free video lesson will show you how. From Ramanujan to calculus cocreator Gottfried Leibniz, many of the world's best and brightest mathematical minds have belonged to autodidacts. And, thanks to the Internet, it's easier than ever to follow in their footsteps (or just finish your homework or study for that next big test). With this installment from Internet pedagogical superstar Salman Khan's series of free math tutorials, you'll learn how to verify this fundamental trigonometric identity.
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How To: Remember "greater than" & "less than" symbols

How To: Use ">" (greater than) and "<" (less than) symbols

How To: Find a number given Its percent

How To: Solve equations with the order of operations

How To: Calculate percent composition for chemistry

How To: Find the area of a parallelogram using geometry

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How To: Find the Volume of Composite Figures (Also Called Composite Shapes)

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How To: Spend Money on a Graphing Calculator? Nah—Just Use This WebBased TI Emulator

How To: Prove a triangle inscribed in a circle is right angled

How To: Find the formula of a piecewise function given a graph

How To: Find the area of a triangle when given 2 sides & angle

How To: Calculate the height and volume of a pyramid

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