In this work, we consider two types of large-scale quadratic matrix equations: Continuoustime algebraic Riccati equations, which play a central role in optimal and robust control, and unilateral quadratic matrix equations, which arise from stochastic processes on 2D lattices and vibrating systems. We propose a simple and fast way to update the solution to such matrix equations under low-rank modifications of the coefficients. Based on this procedure, we develop a divide-and-conquer method for quadratic matrix equations with coefficients that feature a specific type of hierarchical low-rank structure, which includes banded matrices. This generalizes earlier work on linear matrix equations. Numerical experiments indicate the advantages of our newly proposed method versus iterative schemes combined with hierarchical holds for an induced norm · then ϕ J (z) has exactly k eigenvalues (counting multiplicities) in the open unit disc and k eigenvalues with modulus greater than 1, where k denotes the cardinality of J. This implies the result of the lemma.Setting ψ(λ) := −B −1 J (λA J + λ −1 C J ), the condition (30) clearly holds if we can show that the spectral radius ρ(ψ(λ)) is less than 1 for every λ on the unit circle. Note that |λA J + λ −1 C J | ≤ A J +C J because A J , C J are non-negative. Combined with the fact that −B J is an M-matrix, which implies −B −1 J 0, and the monotonicity of the spectral radius, we obtain (1)).Using −B −1 J 0 we also have (A J + B J + C J + I)e e =⇒ (A J + C J )e −B J e =⇒ ψ(1)e e.