We study the oscillation problems for the second order half-linear differential equation [ p ( t ) Φ ( x ′ ) ] ′ + q ( t ) Φ ( x ) = 0 , where Φ ( u ) = | u | r − 1 u with r > 0 , 1 / p and q are locally integrable on R + ; p > 0 , q ⩾ 0 a.e. on R + , and ∫ 0 ∞ p − 1 / r ( t ) d t = ∞ . We establish new criteria for this equation to be nonoscillatory and oscillatory, respectively. When p ≡ 1 , our results are complete extensions of work by Huang [C. Huang, Oscillation and nonoscillation for second order linear differential equations, J. Math. Anal. Appl. 210 (1997) 712–723] and by Wong [J.S.W. Wong, Remarks on a paper of C. Huang, J. Math. Anal. Appl. 291 (2004) 180–188] on linear equations to the half-linear case for all r > 0 . These results provide corrections to the wrongly established results in [J. Jiang, Oscillation and nonoscillation for second order quasilinear differential equations, Math. Sci. Res. Hot-Line 4 (6) (2000) 39–47] on nonoscillation when 0 < r < 1 and on oscillation when r > 1 . The approach in this paper can also be used to fully extend Elbert's criteria on linear equations to half-linear equations which will cover and improve a partial extension by Yang [X. Yang, Oscillation/nonoscillation criteria for quasilinear differential equations, J. Math. Anal. Appl. 298 (2004) 363–373].
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