I've been helping one of my kids with some online high school classes, and we just read through the course material together and work the problems. Despite my having taken those subjects before, all of the material is new to me. I have no memory of learning that stuff in high school, despite graduating with AP classes.

It's nice because I get to learn new things, so I'd recommend that rather than teaching yourself before teaching your child that instead you just learn the material together. If you point out the stuff that is confusing to you and how you find the answer then your kids can learn that process as well.

And I can never remember the formulas for sin, cos, and tangent either so I just keep a graphics book handy.