# Thread: Help me with Completing the square

1. ## Help me with Completing the square

2x^2 = 3x - 7

I understand up to a certain point ;

1. 2x^2 = 3x - 7 ( subtracting 3x )

2. 1/2(2x^2 - 3x ) = 1/2(-7) ( multiplying by 1/2 to make the x^2 - coefficent 1)

3. x^2 - 3/2x = -7/2 ( miltiplying and simplifying )

according to the text it says

x^2 - 3/2x + 9/16 = -7/2 + 9/16 i don't understand how they
got that result

2. You could use the general formula, then it is just a matter of plugging in a,b, and c.

In this case, a=2, b=-3, c=7

$a(x-\frac{b}{2a})^{2}+\underbrace{c-\frac{b^{2}}{4a}}_{\text{constant}}$

3. ## more confused

that formula got me more confused. Can you elaborate on that formula like where you got that from

4. Look at your step 3, to complete the square you need b^2 as missing third item in general formula: (a+b)^2= a^2+2ab+b^2. Your a^2 is x^2, 2ab is 3/2x, which gives you b: 2ab= 3/2x=2* x* 3/4, 3/4 is b, then b^2 is 9/16. If it's missing, add it to both sides and your left side is completed!