cos‌2‌θ=cos‌θ+sin‌θ ⇒(cos2θ−sin2θ)−(cos‌θ+sin‌θ)=0 ⇒(cos‌θ+sin‌θ)(cos‌θ−sin‌θ−1)=0 ⇒cos‌θ+sin‌θ=0 or cos‌θ−sin‌θ=1 When cos‌θ+sin‌θ=0, then tan‌θ=−1 then‌θ=nπ+
3Ï€
4
⇒θ=
3Ï€
4
,
7Ï€
4
∈[0,2π] and when cos‌θ−sin‌θ=1, then sin‌θ+(1−cos‌θ)=0 and 2‌sin‌