............ is credited with giving the first known proof.

Solve the following question using an appropriate Euclid's axiom:
In the figure,we have $AC = DC$ and $CB = CE$. Show that $AB = DE$.

Read the following axioms:
$(i)$ Things which are equal to the same thing are equal to one another.
$(ii)$ If equals are added to equals,the wholes are equal.
$(iii)$ Things which are double of the same thing are equal to one another.
Check whether the given system of axioms is consistent or inconsistent.

In the Book of Elements $1$,how many definitions are given?

The number of dimensions a surface has is:

Euclid stated that all right angles are equal to each other in the form of