Question

$sin2arccos(-\frac{12}{13})$

Answer 1

$sin(2arccos(-\dfrac{12}{13}))=2sin(arccos(-\dfrac{12}{13}))cos(arccos(-\dfrac{12}{13} ))=\\=-\dfrac{24}{13}\cdot\sqrt{1-\dfrac{144}{169}} =-\dfrac{24}{13}\cdot \dfrac{5}{13} =-\dfrac{120}{169}$