Which relation is NOT a function?
please help!! thank youu

The fourth one

Step-by-step explanation:

it can't have the same x value numbers

One way to solve this question is through trigonometry. :)

If you've learnt trigonometry, here are the basic formulas:
SOH CAH TOA (These formulas only apply for right-angled triangles)

Sin(angle) = (Side that is Opposite of angle)/(Hypotenuse)

Cos(angle) = (Side that is Adjacent of angle)/(Hypotenuse)

Tan(angle) = (Side that is Opposite of angle)/(Side that is Adjacent of angle)

In this case, we should use sine of b (the angle at the top of triangle as indicated in your question), where the opposite side is the base (I.e. 4 indicated in your question) and the hypotenuse is 9.

sin(b) = 4/9
{Make angle b the subject of the equation}

{Type this into the calculator}
Angle b = 26.4° (rounded off to 1 decimal place)

Hope this helps! :)