Methods of drawing tangents were invented by Roberval and Fermat... Descartes gave a third method. Of all the problems which he solved by his geometry, none gave him as great pleasure as his mode of constructing tangents. It is profound but operose, and, on that account, inferior to Fermat's. His solution rests on the method of , of which he bears the honour of invention. Indeterminate coefficients were employed by him also in solving bi-quadratic equations.
René Descartes