Khan Academy
Khan Academy: Manipulate Expressions Using Structure
Rewrite an expression containing two unknown variables by choosing a given equation that is equivalent. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video, or receive hints.
Khan Academy
Khan Academy: Algebra: Rational Equations (Advanced)
Solve equations that have one rational expression whose numerator and denominator are polynomial expressions. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video, or receive hints.