1) If sin a = 12/13, then we can use Pythagorean identity to find the value of cos a.
sin^2(a) + cos^2(a) = 1(12/13)^2 + cos^2(a) = 1144/169 + cos^2(a) = 1cos^2(a) = 1 - 144/169cos^2(a) = 25/169cos(a) = ±5/13
Therefore, cos a = 5/13 or cos a = -5/13
2) П\2 is not a standard mathematical notation. It is unclear what operation or question is being asked here. Can you please provide more context or clarify your question?
1) If sin a = 12/13, then we can use Pythagorean identity to find the value of cos a.
sin^2(a) + cos^2(a) = 1
(12/13)^2 + cos^2(a) = 1
144/169 + cos^2(a) = 1
cos^2(a) = 1 - 144/169
cos^2(a) = 25/169
cos(a) = ±5/13
Therefore, cos a = 5/13 or cos a = -5/13
2) П\2 is not a standard mathematical notation. It is unclear what operation or question is being asked here. Can you please provide more context or clarify your question?