This thesis is intended to be a survey on the comparison theorems and oscillation theorems for second order linear differential equations. We shall discuss four comparison theorems in detail: Sturm-Picone, Levin, Reid and Leighton comparison theorems. For oscillation properties, we shall study Hille-Kneser theorems, and Wintner and Leighton oscillation criteria, which involves analysis of a Riccati equation. In 1969, J.S.W. Wong had some deep results about oscillatory and nonoscillatory differential equations. We shall explain these results and some of the examples in detail. This survey is mainly based on the monographs of Swanson [12], and Deng [20], plus a paper of Wong [18]. In some places, we give simplifications and extensions.

This thesis is a short survey for the comparison theorems and oscillation theorems for the second order half-linear equation [c(x)u'^{(p-1)}]'+a(x)u^{(p-1)}=0, where u^{(p-1)}=|u|^{p-2}u. Some examples are also given. The above equation is said to be oscillatory ( O ) if there exists a nontrivial solution having an infinite number of zeros in (0,¡Û); and non-oscillatory ( NO ) if otherwise. Oscillation theorems help to determine whether an equation is ( O ) or ( NO ). These comparison theorem and oscillation theorems give information for the number and position of zeros in (0,¡Û) for a nontrivial solution of the above equation. Materials in this thesis originate from the papers of Li-Yeh and the monograph of Dosly and Rehak. But Reid type comparison theorem is new.

Este trabalho trata de estimativas inferiores para o primeiro autovalor do problema de Dirichlet para o Laplaciano para domínios relativamente compactos contidos em variedades riemannianas. Essas estimativas são obtidas com hipóteses sobre a curvatura seccional ou a curvatura de Ricci radial e a curvatura do bordo do domínio. / This paper deals of lower estimates for the first eigenvalue of the Dirichlet problem for the Laplacian for relatively compact domains contained in Riemannian manifolds. These estimates are obtained with assumptions on the sectional or Ricci radial curvature and the curvature of the boundary of the domain.

Este trabalho trata de estimativas inferiores para o primeiro autovalor do problema de Dirichlet para o Laplaciano para domínios relativamente compactos contidos em variedades riemannianas. Essas estimativas são obtidas com hipóteses sobre a curvatura seccional ou a curvatura de Ricci radial e a curvatura do bordo do domínio. / This paper deals of lower estimates for the first eigenvalue of the Dirichlet problem for the Laplacian for relatively compact domains contained in Riemannian manifolds. These estimates are obtained with assumptions on the sectional or Ricci radial curvature and the curvature of the boundary of the domain.

Este trabalho trata de estimativas inferiores para o primeiro autovalor do problema de Dirichlet para o Laplaciano para domínios relativamente compactos contidos em variedades riemannianas. Essas estimativas são obtidas com hipóteses sobre a curvatura seccional ou a curvatura de Ricci radial e a curvatura do bordo do domínio. / This paper deals of lower estimates for the first eigenvalue of the Dirichlet problem for the Laplacian for relatively compact domains contained in Riemannian manifolds. These estimates are obtained with assumptions on the sectional or Ricci radial curvature and the curvature of the boundary of the domain.