此题用三角代换（换元法）令x=2sint不妨设t∈(-π/2,π/2)∴y=2sint+2|cost| =2sint+2cost t∈(-π/2,π/2)=2√2sin(t+π/4) t∈(-π/2,π/2)∴当t+π/4=π/2即t=π/4时,y取得最大值为2√2当t+π/4=-π/4即t=-π/2时...