How do I find for x when given y?

Question

Given y how do I find for x when c=1?

$1-\sqrt{1-x^2/c^2}$ = y

e.g.

$1-\sqrt{1-.886^2/1^2}$ = y = 0.5363147619

Answer 1

$1-\sqrt {1-\dfrac {x^2}{c^2}}=y$
As $c=1$,
$1-\sqrt {1-x^2}=y$
$\sqrt {1-x^2}=1-y$
$1-x^2=(y-1)^2$
$x^2=1-(y-1)^2$
$x=\sqrt {1-(y-1)^2}$
$x=\sqrt {1-y^2+2y-1}$
$x=\sqrt {2y-y^2}$