... =∈xk,kcos 2x 1x8m,m8h3xx,hcos 1348h 8hDo : k k33để k nguyên ta chọn h 3m m ( thì k 8m ) Caùch khaùc ==π∈⎧⎧⎪⎪⇔⇔=π∈⎨⎨π==⎪⎪⎩⎩cos 2x 1 x k , kx8m,m3x 3kcos 1 cos ... ()⇔=⇔+=⇔+==⎧⇔⎨=⎩⎧−=⇔⎨=⎩⎧=⇔⎨=⎩⇔=⇔=π∈π⇔= ∈22cos 6x cos 2x 11cos 8x cos 4x 12cos 8x cos 4x 2cos 8x 1cos 4x 12cos 4x 1 1cos 4x 1cos 4x 1cos 4x 1cos 4x 14x k2 ,kkx,k2 ... k2 , k 2x k2 , khaycos 6x 1 cos 6x 1 π=∈kx,k2 Caùch khaùc ==⎧⎧⇔⎨⎨==π∈⎩⎩cos8x 1 cos8x 1cos 4x 1 4x k2 , k π⇔= ∈kx,k2 Trường hợp 4: DÙNG KHẢO SÁT HÀM SỐ y = ax...