Common Core
A-CED.A.3
3 lessons teach this standard. Every lesson is interactive, and every one prints as a worksheet with a separate answer key.
Algebra 1 · Chapter 5 · Lesson 3
Two unknowns, two conditions.
Multivariable Calculus · Chapter 6 · Lesson 2
Optimising when you are not free to go anywhere.
Differential Equations · Chapter 7 · Lesson 1
Systems of Differential Equations
Two quantities changing, each depending on the other.