In the image below: - AB and AD are tangent to the circle - BC and AD are parallel
What is the length of AC?
Thank you very much in advance!
Note that $AD=49$ and $BD=28$ by symmetries. Thus $ABD$ is completely determined and from there also $BC$, i.e. the complete figure.
The area of $ABD$ can be found by Heron's formula. That allows you to find the height $h$ of $B$ above $AD$, hence $\frac12 BC$ by Pythagoras from $h$ and $CD$. Finally $AC$ with Pythagoras from $AD+\frac12 BC$ and $h$.