What number should be added to both sides of the equation to complete the square? x^2-40x=0

+40

Step-by-step explanation:

400

Step-by-step explanation:

When completing the square, all you need to do is take half the coefficient of x, and square it.

In this case the coefficient of x is -40, and half of that is -20.  -20 squared is 400, and that is what you need to add to both sides.

Note that when completing the square, you'll always be adding a positive number unless coefficient you're working with is an imaginary or complex number.

a is the right answer