4. The value of 16 cos(2π/15) cos(4π/15) cos(8π/15) cos(16π/15) is(a) 1(b) 3(c) -1(d) None of theseplease explain

i thnk the answer is -1...... 

get a tricks

the no of cos function is 4.........  ans 1/2^4....................  if we multiply 8*2 then its values is 16 which exceeds 15...........  so sign is negative....................  if you like my answer please please approve it...........  its a very good tricks..........

the mod of the value is 1.........  but i dont emember its -1 or +1.........  if it is -1 then its the tricks.............  if it is +! then sign system is applicable for  only sin function............

thanks............  approve it..............