+ x
+ x
= 9000, (7) *
f
= x
+ x
+ x
= 0, (8) *
f
= x
+ x
+ x
= 0, (9) *
f
= x
+ x
+ x
= 12000, (10) *
f
= x
+ x
+ x
= 0, (11) *
f
= x
+ x
+ x
= 0, (12) *
3? (x
+ x
+ x
) = 2? (x
+ x
+ x
), (16) *
2 ? (x
+ x
+ x
) = 4 ? (x
+ x
+ x
), (17) *
4 ? (x
+ x
+ x
) = 3 ? (x
+ x
+ x
), (18) *
3 ? (x