Let P(sin⁡θ,cos⁡θ),(0≤θ≤2π), be a point in a triangle with vertices (0,0),(3/2,0),and(0,3/2). Then,

The equations of lines along OA, OB, and AB are y= 0, x= 0, and x + y =3/2, respectively.Now, P and B will lie on the same side of y: 0 if cos 0 > 0. Similarly,P and A will lie on the same side of x=0 if sin θ> 0, and P and O will lie on the same side of  x + y =3/2if sin⁡θ+cos⁡θ<3/2 Hence, P will lie inside ΔABC if sin⁡θ>0,cos⁡θ>0 and sin⁡θ+cos⁡θ<3/2 now,sin⁡θ+cos⁡θ<32now sin⁡(θ+π4)<34Since  sin⁡θ>0 and cos⁡θ>0,0<θ<π/12 or 5π/12<θ<π/2