If P(6/9,y) is on the unit circle in quadrant IV, then y=

A unit circle is a circle with center at the origin, (0,0), and radius = 1.

Its equation is:  x² + y²  =  1.

Since the x-value is 6/9, the above equation becomes (6/9)² + y²  = 1

--->  (6/9)² + y²  = 1  --->  (2/3)² + y²  = 1   --->   4/9 + y²  = 1   --->    y²  = 5/9

--->   y = √5/3  or  y = -√5/3 

Since the point is in quadrant IV   --->   y = -√5/3