Explicit image of $A_5$ inside $PGL(2,\mathbb{C})$

finite-groupsgroup-presentationgroup-theory

The list of finite subgroups of $PGL(2,\mathbb{C})$ is well known. The cyclic subgroups are easily written down. I was wondering if it is possible to explicitly write down a finite subgroup which is isomorphic to $A_5$. I tried with a presentation of $A_5$ given by

$$
A_5 = \{x,y\ |\ x^5=y^2=(xy)^3=1\},
$$

and tried to find elements of $PGL(2,\mathbb{C})$ which satisfy this relation but I was not successful. What am I missing here? Is there an easier way?

Thank you in advance.

Best Answer

Let $\omega$ be a primitive fifth root of $1$. By a back of the envelope calculation, using traces, I came up with

$$ x \mapsto \left( \begin{array}{cc}\omega&0\\0&\omega^{-1}\end{array}\right),\ \ \ \ x^{-1}y \mapsto \left( \begin{array}{cc}a&b\\1&d\end{array}\right), $$

where $a = 1/(\omega^2-1)$, $b=-a^2-a-1$, $d=-1-a$, and the images are of course to be understood to be modulo the scalar matrices.

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