On the problem of estimation of the number of cycles in two-dimensional quadratic systems from the viewpoint of nonlinear mechanics

Two-dimensional quadratic systems are considered as a Liénard equation with certain special nonlinearities. Theorems on the existence or absence of cycles are given. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 1, pp. 48–57, January, 1998.