RSH, which is -we know that Angle Side Side can be used for any general triangle but it can be, -RSH is essentially Angle Side Side for right triangles, if you have 2 sides of a right triangle and- in common, --if 2 sides of a right triangle are congruent then the 2 triangles are definitely congruent but once you know that two triangles are congruent, then they're corresponding angles have to be congruent, and angle EBD, angle EBD corresponds to angle EBF so we know that angle EBD must be congruent to angle EBF so EBD must be congruent to EBF, well if EBD is congruent to EBF then that means that segment EB must bisect, must bisect angle CBF, or actually CBA even, it could be called CEF angle CBA.