Answer:
 Equation of circle is (x + 1)² + (y - 2)² = 9 .
Step-by-step explanation:
As the standard form of the equation of circle is 
(x-h)² + (y-k)² = r²
Where r represented the circle and (h,k) are the centre of circle .
(This standard form of the circle is similar to Pythagorean theorem 
i.e Hypotenuse² = Perpendicular² + Base²)
As given
A circle has its center at (−1, 2) and a radius of 3 units.
Putting all the values in the equation of circle 
(x-(-1))² + (y-(2))² = 3²
(x + 1)² + (y - 2)² = 9 
Therefore the equation of circle is (x + 1)² + (y - 2)² = 9 .