Well this has multiple answers now doesn't it? You've factored correctly. You know that you're equation will be zero when cos(x)=0 and when 1-2sin(x)=0. So solve for both. I'll start you. The first time cos(x)=0 starting from 0 and moving positively is at and it will do so at every at every after that. So I would write one zero as where k is any integer.