Question 1138396
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{{{sin(theta)}}} = {{{-sqrt(1 - cos^2(theta))}}} = {{{-sqrt(1 - (-2/3)^2)}}} = {{{-sqrt(1 - 4/9)}}} = {{{-sqrt(5/9)}}} = {{{-sqrt(5)/3}}}.


The sign at the square root  is " - " (MINUS), because the angle {{{theta}}} is in QIII, by the condition.
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It is your standard &nbsp;"mantra", &nbsp;which you should pronounce every time, &nbsp;when you solve such a problem.