ques.

consider equilaterla trianlge ABC of side x. drop perpendicular from A to BC.

Let it meet BC at D.

since ABC is an equi triangle, so the perpendicular also becomes the angle bisector of angle A, and perpendicular bisector of BC(this can be proved by showing triangles ADB and ADC cong)

so angle BAD= 1/2[angle BAC]=30 degrees

and

BD=x/2

and

AB=x

 so sin BAD=BD/AB=1/2

Thus,

 Sin 30 =1/2