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4.3 Circles - Arc length and sector area
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The figure presents a circle in the x y plane, with the origin labeled O. The center of the circle lies at the origin. There are 4 points, T, R, Q, and P, labeled clockwise on the circle. Point T lies on the x axis, directly to the left of the origin, and has coordinates negative 1 comma 0. Point R lies above the x axis, and to the left of the y axis. Point Q lies above the x axis and to the right of the y axis. Point P lies on the x axis, directly to the right of the origin, and has coordinates 1 comma 0. Points R and Q appear to be symmetric with respect to the y axis. Four line segments are drawn from the origin to each of the four points on the circle.

In the xy-plane above, points P, Q, R, and T lie on the circle with center O. The degree measures of angles P O Q and R O T are each 30°. What is the radian measure of angle Q O R ?

A.

five sixths, pi

B.

three fourths, pi

C.

two thirds, pi

D.

one third, pi