Area of a regular polygon with $n$ sides each of length $a$ equals —

• a$\dfrac{na^{2}}{4}\cot\dfrac{180°}{n}$
• b$\dfrac{na^{2}}{2}\tan\dfrac{180°}{n}$
• c$na^{2}\cot\dfrac{180°}{n}$
• d$\dfrac{a^{2}}{4}\cot\dfrac{180°}{n}$