Cos(-4x)cos(-x)+sin(-4x)sin(-x)=1
cos4xcosx+sin4xsinx=1
(cos(4x-x)+cos(4x+x))/2 + (cos(4x-x)-cos(4x+x))/2 = 1
(cos3x+cos5x+cos3x-cos5x)/2 = 1
(2cos3x)/2 = 1
cos3x=1
3x=2πn, n∈Z
x=(2πn)/3, n∈Z
(14/3)х-37=1/13
(14/3)х-481/13=1/13
<span>14/13x=482/13
x=482/13*3/14=1446/182=723/91
</span>