Step-by-step answer:
The general form of an equation centered at O(0,0) is given by
x^2+y^2=r^2
where r is the radius, (x,y) is any point on the circumference.
If B(4,5) lies on the circumference, then we can find the radius of the circle by substitution:
4^2+5^2=r^2
=>
r^2 = 16+26 =41
Hence the equation of a circle centred at O(0,0) and B(4,5) on its circumference is
x^2 + y^2 = 41
