HEY vishal , look
learn : length of internal bisector is from A is ( 2bc/b+c) cos A/2
THEREFORE , b option is correct .
first u draw the diagram .
now , u take triangle AED ,
use cosA/2= AD/AE = ( 2BC/B+C) cosA/2 /AE
cancelling cosA/2 , WE GET ,
AE= ( 2 bc /b+c)
hence option (A ) IS ALSO correct......
now ,
again take triangle AED, HERE DE= (2BC/B+C) sin A/2 (USING SINA/2)
AND TAKE TRIANGLE ADF, DF= ( 2bc/b+c)sin A/2
EF= DE+DF =4 bc / b+c sin A/2
hence C IS CORRECT
now DE=DF ( THERFORE TRIANGLE IS ISOCELES)
OPTION D IS ALSO CORRECT..........
ANS ---- A, B , C, D,