In a Triangle ABC if A is the point (1,2)and the equation of the median through B andC are respectively x+y=5 and x=4 then B is

The equation of median through B is x+y = 5. The point B lies on it so the coordinates of B are (x1, 5-x1)
Now CF is a median through C, so coordiantes of F i.e. mid-point of AB are
((x1+1)/2, (5 – x1+ 2)/2)
Now this lies on x = 4 so this means (x1+1)/2 = 4
This gives x1 = 7
Hence, the cooridnates of B are (7, -2).