According to this Circle Equation, all negative symbols give the OPPOSITE terms of what they really are, which is why you see a 3in the parentheses [-(-3) = 3]. So, you plug the center into the formula, where <em>H</em><em> </em>is the <em>phase</em><em> </em><em>shift</em><em> </em>[<em>horizontal</em><em> </em><em>shift</em>] and <em>K</em><em> </em>is the <em>vertical </em><em>shift,</em><em> </em>then square your radius [9= 3²].
Step-by-step explan(A + B)2 = A2 + 2AB + B2 is correct. The area of the large square can be written as (A+B)(A+B) or, by adding up the areas of the two squares and two rectangles inside it, which are A2, B2, AB, and AB.