The approximation indicator "≈" I use for decimal approximations with tilde "~" becoming a rougher approximation. For linear algebra I found the popular suggestion of Hoffman & Kunze to generally be quite useful (although the abstractness arrived as a little bit of a kicker at the outset). For One variable https://codyxuqmg.howeweb.com/37050814/a-simple-key-for-por-qué-es-bueno-leer-el-tarot-unveiled