If 2cos (((5π)/4)+3x)cos ((π/4)+3x)=0 and
sin (2x−2y)=cos y where (π/4)≤x≤(π/2) and
(π/4)≤y≤(π/2) . find the value of { ((sin (2x+y))),((cos (2x+y))),((cos (2x−y))),((sin (2x−y))) :}
A class has 13 children. To play a
game one child is the referee and the
other children are divided in three
teams with four children in each team.
In how many ways can the class play
the game?