Question

sin 17п/6+cos 240

4sin7п/12*cos7п/12

cos18 +cos 42/cos 12

Answer 1

1/2 + (-1/2) = 0

 

4*( 2 sin 7π/6) = 2 * ( 2 * (-1/2) ) = -2

 

по формулам суммы 

(2cos60/2*cos24/2) / cos12 =( 2cos30*cos12)/cos12 = 2cos30 = 2*√3/2=√3