Im doing this presentation for school and we have to find out who exactly first used independent and dependent variables. I've searched everywhere but no answer was found its either John radford young or Marshall.
Have you seen the Earliest Known Uses of the Word of Mathematics. https://jeff560.tripod.com/d.html
The point is that this might be first English usage? What about German or French?
"DEPENDENT/INDEPENDENT VARIABLE. Independent variable appears in 1813 in Memoirs of the Analytical Society (Cambridge): “The method of Laplace for reducing an equation of the first order, where the difference of the independent variable is any function of the variable itself, to one wherein that difference is constant, is well known.” [Google print search by James A. Landau]
Subordinate variable and independent variable appear in English in the 1816 translation of Differential and Integral Calculus by Lacroix: "Treating the subordinate variables as implicit functions of the indepdndent [sic] ones" [OED].
Dependent variable appears in in 1831 in the second edition of Elements of the Differential Calculus (1836) by John Radford Young: "On account of this dependence of the value of the function upon that of the variable the former, that is y, is called the dependent variable, and the latter, x, the independent variable" [James A. Landau].
In Statistics R. A Fisher used the terms dependent and independent in his presentation of regression analysis: see Section 25 of Statistical Methods for Research Workers (1925) on "Regression coefficients". For Fisher these terms qualified variate but later writers have generally favoured variable.