Step-by-step explanation:
when we look at the triangle try to reposition it at least in your mind to make R to be the center of the circle. then RP (29) is the radius of the circle and the angle indication of the angle R in this circle.
then we see QP is the sine, and RQ is the cosine of the angle R. but don't forget : all are multiplied by the radius, because the pure sin and cos functions deliver the values for the standard circle with radius 1.
so,
QR = cos(R)×RP
21 = cos(R) × 29
cos(R) = 21/29
the fourth answer is correct.
