+57 Consider \(\triangle ABC\) with \(AB = 5\) and \(BC = 6\). Let \(D\) be a point on \(AC\) such that \(CD = 2AD\) and \(\angle CBD = 2\angle ABD\), as in the picture below:
Find length \(AC\).
Any help would be greatly appreciated 
+13 I think you kind of have an idea of what this problem is about based on the title of your question. Try using the law of cosines first.
