Deflection of Cantilever Beams | Area-Moment Method

Generally, the tangential deviation t is not equal to the beam deflection. In cantilever beams, however, the tangent drawn to the elastic curve at the wall is horizontal and coincidence therefore with the neutral axis of the beam. The tangential deviation in this case is equal to the deflection of the beam as shown below.
 

From the figure above, the deflection at B denoted as δ_B is equal to the deviation of B from a tangent line through A denoted as t_B/A. This is because the tangent line through A lies with the neutral axis of the beam.