ban son93 ui, tui thay bai ban giai hoi co van de ak, co nhiu cho tui k hieu, ban dat t=sinx=> dt=cosxdx vay thi phuong trinh cua ban phai la can t chia can 1-t^2 chu, con neu ban dat t=sinx => dt=cosxdx roi ban chuyen ve thanh dt/cosx=dx thi phuong trinh cua ban phai la can t chia (1-t^2) chu. tai sao ban suy ra phuong trinh ngo vay? minh k hieu y tuong cua ban cho lam, ban noi ro hon ti di