The graph of $ f $ is given. State, with reasons, the numbers at which $ f $ is $ not $ differentiable.
So we're given this graph of this function and were asked where this function F is not differentiable. Okay. So what we can see is that this is a smooth curve all the way through Until we get to x equals four. At which time we have this corner. That happens right? So at x equals four. Yeah. Is not differential. Remember the derivative have prime is the slope of the tangent line at that X. Well, the problem is with this corner here, there is no tangent line there And x equals four. There is no tangent line due to the corner happening the sharp turn until therefore it is not differentiable. At X equals four.