sat suite question viewer
What is the value of ?
Explanation
Choice A is correct. A trigonometric ratio can be found using the unit circle, that is, a circle with radius unit. If a central angle of a unit circle in the xy-plane centered at the origin has its starting side on the positive x-axis and its terminal side intersects the circle at a point , then the value of the tangent of the central angle is equal to the y-coordinate divided by the x-coordinate. There are radians in a circle. Dividing by yields , which is equivalent to . It follows that on the unit circle centered at the origin in the xy-plane, the angle is the result of revolutions from its starting side on the positive x-axis followed by a rotation through radians. Therefore, the angles and are coterminal angles and is equal to . Since is greater than and less than , it follows that the terminal side of the angle is in quadrant II and forms an angle of , or , with the negative x-axis. Therefore, the terminal side of the angle intersects the unit circle at the point . It follows that the value of is , which is equivalent to . Therefore, the value of is .
Choice B is incorrect. This is the value of , not .
Choice C is incorrect. This is the value of , not .
Choice D is incorrect. This is the value of , not .