Question 1159519
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This truly is basic; a thorough understanding of this kind of question is necessary as you get deeper into the study of trigonometry.<br>
You can use the unit circle or the graph of the sine function to find the answer; you should be able to do it either way.<br>
With the unit circle, the sine of an angle is the y value.  On the unit circle, what is the only angle at which the y value is -1?<br>
With the graph of the sine function, on a full period 0 to 2pi radians, the graph starts at 0, rises to its maximum value of 1 at pi/2 radians, returns to 0 at pi, falls to its minimum value of -1 at 3pi/2 radians, and returns to 0 at 2pi.  Again there is only one angle for which the value of the sine function is -1.<br>
I again emphasize that if you are just starting your study of trigonometry you want to have a thorough understanding of the sine, cosine, and tangent functions in relation to the unit circle and to the graphs of those functions.<br>