Given CD is an altitude such that AD=BC , AB=3 cm and CD= √2 cm.
Let AD=x, Since given AB=3
AD+DB=3
x+DB = 3
DB = 3-x
Since ΔBCD is rght angle triangle, let's apply Pythagoras theorem
Since given AD=BC,let us plugin BC=x in above step.
6x=11
x=
Now we know AD=x= and given CD=√2.
Let us apply Pythagoras theorem for ΔACD
= 2.315cm