(r + 3) / ( r - 2) = (r - 1) / ( r + 1) cross-multiply
(r + 3) ( r + 1) = (r - 2) (r - 1) simplify
r^2 + 4r + 3 = r^2 - 3r + 2 subtract r^2 from both sides
4r + 3 = -3r + 2 add 3r to both sides, subtract 3 from both sides
7r = - 1 divide both sides by 7
r = - 1/7
