Ответы и объяснения

2013-04-06T12:34:19+00:00

1) сos780 = cos(360 + 60) = cos60 = 1/2 = 0.5

2) sin 13П/6 = sin(П/2 + 5П/6) = sin(5П/6) = 1/2 = 0,5

3) sina = sqrt(1 - (-12/13)^2) = sqrt(1 - 144/169) = sqrt(25/169) = 5/13

sina = 5/13