If $\frac{\cos \alpha}{\cos \beta}+\frac{\sin \alpha}{\sin \beta}=-1$, find $\frac{\cos^3\beta}{\cos \alpha}+\frac{\sin^3\beta}{\sin \alpha}$. 
If $\displaystyle \frac{\cos \alpha}{\cos \beta}+\frac{\sin \alpha}{\sin \beta}=-1$, find $\displaystyle \frac{\cos^3\beta}{\cos \alpha}+\frac{\sin^3\beta}{\sin \alpha}$.

I tried$$
\sin(\alpha+\beta)=-\sin \beta \cos \beta,\\
2\sin(\alpha+\beta)=-\sin (2\beta),$$
and $$\frac{\cos^3\beta}{\cos \alpha}+\frac{\sin^3\beta}{\sin \alpha} =\frac{\sin\alpha\cos^3\beta+\sin^3\beta \cos \alpha}{\sin \alpha \sin \alpha},$$
but unable to find that ratio.
Any help, please.

$\def\peq{\mathrel{\phantom{=}}{}}$Denote $γ = α + β$, then$$
\frac{\cos α}{\cos β} + \frac{\sin α}{\sin β} = -1 \Longrightarrow \sin γ = \sin(α + β)  = -\sin β\cos β.
$$
Thus,$$
\sin(γ - β) = \sin γ\cos β - \cos γ\sin β = -\sin β\cos^2 β - \cos γ\sin β,\\
\cos(γ - β) = \cos γ\cos β + \sin γ\sin β = \cos γ \cos β - \sin^2 β\cos β.
$$
Now, note that$$
1 = (\sin^2 β + \cos^2 β)^2 \Longrightarrow \sin^4 β + \cos^4 β = 1 - 2\sin^2 β\cos^2 β,
$$
then\begin{align*}
&\peq \frac{\cos^3 β}{\cos α} + \frac{\sin^3 β}{\sin α} = \frac{\cos^3 β}{\cos(γ - β)} + \frac{\sin^3 β}{\sin(γ - β)}\\
&= \frac{\cos^3 β}{\cos γ \cos β - \sin^2 β\cos β} + \frac{\sin^3 β}{-\sin β\cos^2 β - \cos γ\sin β}\\
&= \frac{\cos^2 β}{\cos γ - \sin^2 β} - \frac{\sin^2 β}{\cos γ + \cos^2 β}\\
&= \frac{\cos^2 β(\cos γ + \cos^2 β) - \sin^2 β(\cos γ - \sin^2 β)}{(\cos γ - \sin^2 β)(\cos γ + \cos^2 β)}. \tag{1}
\end{align*}
Because\begin{align*}
&\peq \cos^2 β(\cos γ + \cos^2 β) - \sin^2 β(\cos γ - \sin^2 β)\\
&= (\cos^2 β - \sin^2 β)\cos γ + \sin^4 β + \cos^4 β\\
&= \cos 2β\cos γ + 1 - 2\sin^2 β\cos^2 β,
\end{align*}
and\begin{align*}
&\peq (\cos γ - \sin^2 β)(\cos γ + \cos^2 β)\\
&= \cos^2 γ + (\cos^2 β - \sin^2 β)\cos γ - \sin^2 β\cos^2 β\\
&= (1 - \sin^2 γ) + \cos 2β\cos γ - \sin^2 β\cos^2 β\\
&= (1 - \sin^2 β\cos^2 β) + \cos 2β\cos γ - \sin^2 β\cos^2 β\\
&= \cos 2β\cos γ + 1 - 2\sin^2 β\cos^2 β,
\end{align*}
then $(1) = 1$, i.e.$$
\frac{\cos^3 β}{\cos α} + \frac{\sin^3 β}{\sin α} = 1.
$$
