so this is from a calculus problem but i'm not sure how to achieve the other angle (240 degrees). I know you get the (120 degrees from reference angle (180-60 = 120) but for 240 i'm not sure. Thanks and heres the problem.

t=\left\{\begin{array}{c}\frac{2\pi}{3}\\{}\\\frac {4\pi}{3}\end{array}\right.\,+2\pi

k\,,\,\,k\in\mathbb{z}

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t=\left\{\begin{array}{c}\frac{2\pi}{3}\\{}\\\frac {4\pi}{3}\end{array}\right.\,+2\pi

k\,,\,\,k\in\mathbb{z}

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how would i go about achieving the ?

Thanks.