Algebra 2
Quadratics through logarithms, with answers graded on form as well as value.
1,473 interactive problems, free to use.
The second algebra course, covering the function families that precalculus and the SAT both rely on. When a problem asks students to factor, expand, or simplify, the grader checks the form of the answer as well as its value, so copying the question back does not pass.
Word problems and modelling questions include full worked solutions.