Sal solved a few examples where we need to evaluate an expression, but we don't know the individual variable values.
Expressions with unknown variables is a free educational video by Khan Academy.It helps students in grades 9,10,11,12 practice the following standards HSA.SSE.A.2.
1. HSA.SSE.A.2 : Use the structure of an expression to identify ways to rewrite it. For example, see x4 - y4 as (x2)2 - (y2)2, thus recognizing it as a difference of squares that can be factored as (x2 - y2)(x2 + y2)..