4sinx + 2cosx=0 sin5x sinx - cos5x cosx=1\2 cos7x + cos3x=0

1)2tgx+1=0; 2tgx=-1; tgx=-1/2; x=-arctg0,5+πn
2)-(cos5x cosx-sin5x sinx)=1/2
  -cos(5x+x)=1/2
  cos6x=-1/2
 6x=+-(π-π/3)+2πn
6x=+-(2π/3)+2πn
x=+-π/9+π/3 *n
3)2cos((7x+3x)/2) *cos((7x-3x)/2)=0
   2cos5x cos2x=0
  cos5x=0       ili           cos2x=0
  5x=π/2 +πn                  2x=π/2+2πn
 x=π/10+π/5 *n                  x=π/4 +πn