Question

The principle solutions of the $Cos\theta =-\frac{1}{2}$ are

• A. $\pi /4$
• B. $2\pi /3$
• C. $4\pi /3$
• D. $\frac{7\pi }{6}$

Answer 1

Answer: (B), (C)

The correct options are
B $2\pi /3$
C $4\pi /3$

The principle solution is the solution of trignometric angle in [0,2$\pi$]

So Two principle solution of above equation are ($\pi$-$\frac{\pi }{3}$) and ($\pi$+$\frac{\pi }{3}$)=$\frac{2\pi }{3}$ and $\frac{4\pi }{3}$