Math and Calculus Tutorials Online
Good one: Solving Ordinary (one variable) Differential Equations
https://people.revoledu.com/kardi/tutorial/ODE/WhatisODE.htm
Using Numerical Methods: https://people.revoledu.com/kardi/tutorial/ODE/Euler%20Method.htm
Introduction to Differential Equations
https://analyzemath.com/calculus/Differential_Equations/introduction.html
Mathematical methods for economic theory (+Optimization)
https://mjo.osborne.economics.utoronto.ca/index.php/tutorial/index/1/toc
Calculus Tutorials:
https://www.midnighttutor.com/
https://www.midnighttutor.com/math_tutor_online.php
Math Tutorials:
https://tutorial.math.lamar.edu/
Math Cheat Sheets:
https://tutorial.math.lamar.edu/Extras/CheatSheets_Tables.aspx#CalcSheet
FIRST-ORDER DIFFERENTIAL EQUATIONS
https://math.hmc.edu/calculus/hmc-mathematics-calculus-online-tutorials/differential-equations/first-order-differential-equations/
