Khan Academy
Khan Academy: Algebra: Rearrange Formulas to Isolate Specific Variables
This video demonstrates how to take the formula for the area of a triangle and rewrite it in terms of height. [2:29]
Khan Academy
Khan Academy: Algebra: Solving for a Variable
This video demonstrates how to solve for a variable. It uses the formula for the perimeter of a quadrilateral and shows how to solve for the variable l. [1:24]