Answer:

And solving for x we got:


And taking square root we got:

Step-by-step explanation:
For this case we have the following point given 
And we want to find the value of x, since P lies on the unitray circle if we find the distance from P to the center of the unitary circle (0,0) we need to get 1. Using the definition of Euclidean distance that means:

And if we square both sides of the last equation we got:

And solving for x we got:


And taking square root we got:
