Answer:
In degrees: -270°, 90°, 450°.
In radians: -3π/2, π/2, 5π/2.
Explanation:
The cosine is always zero where the sine is 1. The sine is 1 at an angle of 90°, and every integer number of 360° added (or subtracted) to that. The corresponding point on the unit circle is (0, 1), labeled A in the diagram.
The angle from the x-axis to the positive y-axis can be called any of ...
... 90°
... -270°
... 450°
... 810°
... π/2 radians
... -3π/2 radians
... 5π/2 radians
... 9π/2 radians
You are asked to pick three of these (or some others you may choose) so that you have 3 different names for the angle to this point.
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Comment on the second figure
The graphing calculator easily shows places where function values are zero. To show where sin(x) = 1, we rewrite it as sin(x) -1 = 0. Then, the zeros are highlighted. In degrees, the ones shown are -270°, 90°, 450°, 810°. You can see that cos(x) is zero at those same angles.