The ordinates of both B & C are 0.
So, BC= (abscissa of B−abscissa of C)=(5−1)=4units=a
The side of equilateral ΔABC.
Now, ΔABC is equilateral and BC is on the x-axis.
So, the abscissa of A will be the mid point of BC.
The ordinate of A will be the height of ΔABC from the mid point of BC.
∴ The coordinates of A are (3,23)