Match the x-coordinates with their corresponding pairs of y-coordinates on the unit circle.
y=+- square root 5 over 3
y=+- square root 7 over 3
y=+- 3 over 3
y=+- 2 square root 2 over 2

y=+- square root 5 over 3

y^2 + x^2 = 1 => x^2 = 1 - y^2 = 1 - 5/9 = 4/9 => x = +/- 2/3

x = +/- 2/3

y=+- square root 7 over 3

y^2 + x^2 = 1 => x^2 = 1 - y^2  =  1 - 7/9 = 2/9 => x = +/- (√2) / 3

x = +/-(√2)/3

y=+- 3 over 3

x^2 = 1 - y^2 = 1 - 3/9 = 1 - 1/3 = 2/3 => x = +/-(√2/3)

x = +/-√(2/3)

y=+- 2 square root 2 over 2

= y = +/- 2(√2) /2 = √2  these y-coordinates are out of the unit circle, then there is not a corresponding x - coordinate for them.

Your maths is very weak try yourself this would improve your skills don't depend on others