Question

what is the least number of squares which must be shaded to make the given figure symmetric along the dotted line

Answer 1

the two objects of  same type , same length , same angle are called symmetric to each other

in other words two identical objects are called symmetric to each other.

for example

two square with equal length of sides and angles are called symmetric to each other.

two objects of same length in lying same direction i.e 50m lying in horizontal direction are called symmetric to each other.