Answer
$\cot(y)=\frac{{x}}{\sqrt {1-x^{2}}}$
Work Step by Step
Using Pythagoras's theorem, the third side, $k$, of this right angled triangle can be found:
$1^{2}=x^{2}+ k^{2}$
$k^{2}=1-x^{2}$
$k=\sqrt {1-x^{2}}$ (since $k\gt0$
Using the triangle given in the diagram, the equation for $\cot(y)=\frac{adjacent}{opposite}$
opposite $=\sqrt {1-x^{2}}$, adjacent $=x$
Therefore $\cot(y)=\frac{{x}}{\sqrt {1-x^{2}}}$
