It appears after lam ==
solve([diff(P,x) == 0, diff(P,y) == 0], x, y, lam)
[[x == 816.8214285714286, y == 506.0324074074074, lam == r5], [x == -816.2645502645503, y == -514.5402298850574, lam == r6], [x == (13.33265402759081 + 1414.015105182754*I), y == (3.906674551362281 - 883.7900965450355*I), lam == r7], [x == (13.33265402759081 - 1414.015105182754*I), y == (3.906674551362281 + 883.7900965450355*I), lam == r8]]
