Tập xác định của hàm số: y = (x+1)/tan3x là: D = R \ {k.2pi/3; k thuộc Z}

A. $\mathrm{D}=\mathrm{ℝ}\backslash \left\{\mathrm{k}\frac{2\mathrm{\pi }}{3}|\mathrm{k}\in \mathrm{\mathbb{Z}}\right\}.$

B. $\mathrm{D}=\mathrm{ℝ}\backslash \left\{\frac{\mathrm{\pi }}{6}+\mathrm{k}\frac{\mathrm{\pi }}{3};\mathrm{k}\frac{\mathrm{\pi }}{3}|\mathrm{k}\in \mathrm{\mathbb{Z}}\right\}.$

C. $\mathrm{D}=\mathrm{ℝ}\backslash \left\{\frac{\mathrm{\pi }}{6}+\mathrm{k}\frac{2\mathrm{\pi }}{3};\mathrm{k}\frac{2\mathrm{\pi }}{3}|\mathrm{k}\in \mathrm{\mathbb{Z}}\right\}.$

D. $\mathrm{D}=\mathrm{ℝ}\backslash \left\{\mathrm{k}\frac{2\mathrm{\pi }}{3}|\mathrm{k}\in \mathrm{\mathbb{Z}}\right\}.$