4+sinx•cosx=7cos²x
4(sin²x+cos²x)+sinxcosx-7cos²x=0
-3cos²x+4sin²x+sinxcosx=0; :|cos²x≠0
4tg²x+tgx-3=0
tgx=t
4t²+t-3=0
D=1+48=49=7²
t=(-1±7)/8
t1=-1;,t2=3/4
tgx=-1;x=-π/4+πk
tgx=3/4;x=arctg3/4+πk;k€Z
2)sin3x=4sinxcos2x
sin3x=1/2(sin3x+sin(x-2x))
sin3x-1/2*sin3x+sinx=0
1/2*sin3x+sinx=0
1/2(3sinx-4sin³x)+sinx=0
3/2*sinx-2sin³x+sinx=0
5/2*sinx-2sin³x=0
sinx(5/2-2sin²x)=0
sinx=0;x=πn
sin²x=5/2:2=5/4
|sinx|=√5/2;х€∅