2cos4x-2sinxcos3x-2sin3xcosx=0
2cos4x-2(sin3xcosx+cos3xsinx)=0
2cos4x-2sin(3x=x)=0
2cos4x-2sin4x=0/2cos4x≠0
1-tg4x=0
tg4x=1
4x=π/4+πn,n∈Z
x=π/16+πn/4,n∈Z
sin(70+x+20-x)/cos(70+x)cos(20-x)=2
sin90/cos(70+x)cos(20-x)=2
1/cos(70+x)cos(20-x)=2
cos(70+x)cos(20-x)=1/2
1/2(cos(70+x-20+x)+cos(70+x+20-x))=1/2
cos(50-2x)+cos90=1
cos(50-2x)=1
sin(40+2x)=1
40+2x=90+360*n,n∈Z
2x=50+360*n,n∈Z
x=25+180*n,n∈Z