Question

(step by step) please explain to me how to complete square for example: x^2+3x+9=0 and please give more examples and explain. thanks :)

Answer 1

http://www.youtube.com/watch?v=xGOQYTo9AKY

Answer 2

x^2+ bx = (x+b/2)^2 - (b/2)^2
Substitute it in xD

Answer 3

Possible intermediate steps:
x^2+3 x+9 = 0
Subtract 9 from both sides:
x^2+3 x = -9
Add 9/4 to both sides:
x^2+3 x+9/4 = -27/4
Factor the left hand side:
(x+3/2)^2 = -27/4
Take the square root of both sides:
abs(x+3/2) = (3 i sqrt(3))/2
Eliminate the absolute value:
x+3/2 = -(3 i sqrt(3))/2 or x+3/2 = (3 i sqrt(3))/2
Subtract 3/2 from both sides:
x = -3/2 i (-i+sqrt(3)) or x+3/2 = (3 i sqrt(3))/2
Subtract 3/2 from both sides:
x = -3/2 i (-i+sqrt(3)) or x = 3/2 i (i+sqrt(3))