Here, Angle DAF is equal to angle CBG.
We know, Sum of all angles in a triangle is equal to 180 degree which is a constant value.
C & D are perpendiculars, Hence they are equal in their magnitude.
Now, F is the remaining angle in Triangle ADF & G is in Triangle BCG.
So, by ASA Postulate, the two mentioned triangles would be Congruent to each other.
Hope this helps!
