【正确答案】∫₀^nπx｜cosx｜dx=∫₀^π｜cosx｜dx+∫_π^2πcosx｜dx+…+∫_(n-1)π^nπx｜cosx｜dx，
∫₀^πx｜cosx｜dx=∫₀^π｜cosx｜dx=cosxdx=π，
∫_π^2πx｜cosx｜dx∫₀^π(t+π)｜cost｜dt=∫₀^πt｜cost｜dt+π∫₀^π｜cost｜dt=π+2π=3π，
∫_2π^3πx｜cosx｜dx