
Dayv O. answered 11/26/22
Caring Super Enthusiastic Knowledgeable Trigonometry Tutor
by observation after solving
if cos(x)=1, then sin(x)=0 and equation is solved
have cos2(x)+1+2sin(x)+sin2(x)=2cos(x)+2cos(x)sin(x)
same as
2+2sin(x)=2cos(x)+2cos(x)sin(x)
means cos(x)=1
happens once per cycle,
at x=zero, at x=2*pi, at x=-2*pi, ....
the problem probably means to specify 0≤x<2*pi