If the point P(-4/5,y) lies on the unit circle and P is in the third quadrant, what does y equal? If necessary, use the slash mark ( / ) for a fraction bar.
We use the fact that x2+y2=1 This is the equation of the unit circle. We know that x=-4/5, so plug this in and solve for y x2+y2=1 (−4/5)^2+y2=1 16/25+y2=1 y2=1−16/25 y2=9/25 y=−square root of 9/ 25 y = -3/5
