摘要
The author proves that any quadratic system in the plane can be changed into the quadratic system （E<sub>1</sub>） or （E<sub>2</sub>） by means of linear transformations, and then gives a necessary and sufficient condition for the systems （E<sub>1</sub>） and （E<sub>2</sub>） to be bounded for t≥0 and to have precisely one monotone unboundol orbit for t≥0 respectively.
The author proves that any quadratic system in the plane can be changed into the quadratic system (E_1) or (E_2) by means of linear transformations, and then gives a necessary and sufficient condition for the systems (E_1) and (E_2) to be bounded for t≥0 and to have precisely one monotone unboundol orbit for t≥0 respectively.
