The range is the set of all y-coordinates of the points in the graph.
The graph is a wavy function that has a maximum y-coordinate of 1 and a minimum y-coordinate of -1. The y-coordinates can also be all numbers between -1 and 1. Choice A. is only the two numbers -1 and 1. That is not correct since the range comprises the numbers -1, 1, and all numbers in between -1 and 1.
The ratios of sides in a 30°-60°-90° triangle are such that the hypotenuse (AB) is double the length of the shortest side (AC). In your triangle, AC is the hypotenuse of similar triangle ACD, which has AD as its shortest side.
