If using the method of completing the square to solve the quadratic equation
x2 + 15x + 21 = 0, which number would have to be added to "complete the
square"?

g(x) = x² + 2

step-by-step explanation:

it is given that the graphs are the same shape.

the only difference is that the red graph is 2 units higher than the blue graph.

that is to say that the red graph is simply the blue graph that has been moved vertically by 2 units in the positive y direction.

hence

g(x) = f(x) + 2

or

g(x) = x² + 2

i think the correct option is the second option.

use distributive property on all like terms and change your signs if you have a double negative or if you have positive/negative