Find the eigenvalues for a matrix which is a product of matrices Suppose I have a matrix $A \in \mathbb{R}^{2, 2}$ which is the product of $3$ other matrices, lets call them $A_1 = \left(\begin{matrix} cosx & -sinx \\ sinx & cos x\end{matrix}\right)$, $A_2= \left(\begin{matrix} 3 & 0 \\ 0 & 7\end{matrix}\right)$ and $A_3 = \left(\begin{matrix} cosx & sinx \\ -sinx & cos x\end{matrix}\right)$. So the situation is:
$$A = A_1 \cdot A_2 \cdot A_3$$
Now, I am asked to find the eigenvalues for this matrix $A$ without multiplying $A_1$, $A_2$ and $A_3$. 
In general, if we assume that we don't want zero eigenvectors, then we can find the eigenvalues solving the characteristic polynomial, which can be found by assuming (actually it is a consequence) that:
$$\det{(\lambda \cdot I - A)} = 0$$
Then we solve for $\lambda$.
Now, my situation is the following:
$$\det{(\lambda \cdot I - A_1 \cdot A_2 \cdot A_3)} = 0$$
I have found the determinant of $A$, using a property of the determinants, but I don't see any property that can help me to find the determinant just above...

Hint 
$$\det (\lambda I -A_1A_2A_1^{-1})=\det (\lambda A_1A_1^{-1} -A_1A_2A_1^{-1}) = \det ( A_1 (\lambda I -A_2)  A_1^{-1}) \\= \det (A_1) \det (\lambda I -A_2) \det (A_1^{-1})$$
