Answer:
Option B. x^2+4=9
Explanation:
You can complete the square when the equation has the form:
ax^2+bx with "a" and "b" different of zero.
In equation A. x^2+4x=9; a=1 and b=4 are different of zero. We can solve the equation by completing the square.
In equation B. x^2+4=9. If we subtract 4 from both sides of the equation:
x^2+4-4=9-4→x^2=5; a=1 but b=0, then we cannot solve the equation by completing the square.
In equation C. x^2+3x=0; a=1 anb b=3 are different of zero. We can solve the equation by completing the square.
In equation D. x^2+4x=x+9
If we subtract x from both sides of the equation:
x^2+4x-x=x+9-x→x^2+3x=9; a=1 and b=3 are different of zero. We can solve the equation by completing the square.