For the following value of $\displaystyle cos \theta$, determine the radian value of $\displaystyle \theta$
a) -1/2
First I found y from the equation $\displaystyle r^2=x^2+y^2$
y= +- \sqrt{y}
My graph therefore is in the 1 and 2 quadrant due to y having + and - values
then i found inverse cos^-1 (1/2) = 1.05
so: pi - 1.05 or 1.05
However the answer according to the book is (4pi)/3