How I construct a segment $a^2$? The length of a segment is given. How can we construct a segment equal to the square of the given segment?

Revised attempt:
1) Construct a $\triangle DBC$ with :
$|DB|=1;$ $ \angle BDC =90°$; $|DC|=a$ .
2) Construct a right angle at $C$, with one leg $BC$.
The other leg of this angle intersects $BD$ 
at $A$, I.e $\angle BCA =90°$.
3) We have :
$|AD| \cdot 1 = a^2.$
