7sin2x-4sin2x+cos2x=0

Question

7sin2x-4sin2x+cos2x=0

Answer 1

3sin 2x+cos 2x=0 |(:cos 2x)
3tg 2x+1=0
3tg 2x=-1
tg 2x=-1/3
2x=arctg(-1/3)+πn
x=-1/2arctg 1/3+(πn)/2