![enter image description here](https://i.stack.imgur.com/C2HG4.jpg)

Hey everyone, I need help with questions on hyperbolic functions.
I was able to do part (a). 

I proved for $\sinh(3y)$ by doing this:

\begin{align\*}
\sinh(3y) &= \sinh(2y +y)\\
&= \sinh(2y)\cosh(y) + \cosh(2y)\sinh(y)\\
&= 2\sinh(y)\cosh(y)\cosh(y) + (\cosh^2(y)+\sinh^2(y))\sinh(y)\\
&= 2\sinh(y)(1+\sinh^2(y)) + (1+\sinh^2(y) + \sinh^2(y))\sinh(y)\\
&= 2\sinh(y) + 2\sinh^3(y) + \sinh(y) +2\sinh^3(y)\\
&= 4\sinh^3(y) + 3\sinh(y).
\end{align\*}

Therefore, $0 = 4\sinh^3(y) + 3\sinh(y) - \sinh(3y)$.

I have no clue what to do for part (b) and part (c) but I do see similarities between part (a) and part(b) as you can subtitute $x = \sinh(y)$.

But yeah, I'm stuck and help would be very much appreciated.