Boundaries of surfaces are:

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

How many dimensions does a line have?

Solve the following question using appropriate Euclid's axiom:
It is known that $x+y=10$ and that $x=z$. Show that $z+y=10$.

State whether the following statement is True or False. Justify your answer.
Attempts to prove Euclid's fifth postulate using the other postulates and axioms led to the discovery of several other geometries.

If $P$,$Q$,and $R$ are three points on a line,and $Q$ lies between $P$ and $R$ [see figure],then prove that $PQ + QR = PR$.