Solution :
Trigonometry is that branch of mathematics which is used to study the relationship between the angles and the lengths of the sides of a triangle.
We known that the co-ordinate of a point on the circumference of a circle making an angle θ with the horizontal having a unit radius is given by :
(1 cos θ, 1 sin θ).
And for any angle made by sin θ on the x - axis is 0 and on the y -axis is 1 or -1 depending on the quadrant.
Since, angle 270 degree falls on the 3rd quadrant, therefore, the value of the co-ordinates of the point is (cos θ, sin θ) = (0,-1).
So the value of sin 270° = -1.
One other example of sin θ = 1 is 90° as 90 degree falls in the first quadrant.