23S A ConJeHure, See. 
tion qx-x^-r as has been found for the refolution of the 
equations x z +qx=r and x^-qx-r, can be obtained by 
means of that fubftitution. 
/ j 
Art, 17. Thefe are the methods of inveftigation by 
which I conceive it to be probable, that cardan’s rules 
for the refolution of the cubic equations x i +qx=r and 
x z ~qx~r , together with the limitation of the rule re- 
lating to the latter of thofe equations, and their inappli- 
cability to the third equation qx-x z =r, may have been 
difeovered by the firft inventor of them. 
