Lamarr and Anthiel received a patent in 1941, but the enormous significance of their invention was not realized until decades later. It was first implemented on naval ships during the Cuban Missile Crisis and subsequently emerged in numerous military applications.
Cash back credit card reward programs started out rather simply, offering a flat percentage rate (typically 1 percent of purchases) rebated back to the customer in the form of a check at the end of the year or a statement credit.
If you are able to find a cash-back card with a greater rate of return than a card that directly repays the loan, you can simply make loan payments using those funds. One way is to track your cash-back rewards each month and make an identical loan payment.