Use completing of the square to find d:$$x^2-dx+5$$

Question

lgbasallote · Answer

you want to turn this into a perfect square trinomial?

anonymous · Answer

Well, actually I just made that up... but I wanted to know how you would be able to find dx of a polynomial when given ax^2-bx+c, ax^2 and c

lgbasallote · Answer

oh nice question...you know that if you are given ax^2 + bx + c then (b/2)^2 = c right?

anonymous · Answer

Yes and thank you.

lgbasallote · Answer

so this time your b is d and c is 5 so $$\large (\frac{d}{2})^2 = 5$$
$$\large \frac{d}{2} = \sqrt 5$$
$$\large d = 2\sqrt 5$$
got it?

anonymous · Answer

Yup...

anonymous · Answer

But can you do it on an hard example with integers or whole numbers...

lgbasallote · Answer

$$2x^2 - bx + 32$$
try it :)

anonymous · Answer

$$4\sqrt{8}$$

lgbasallote · Answer

nope! :p you should get a whole number ;)

anonymous · Answer

b is still irrational :(

lgbasallote · Answer

remember in completing the square method it should be in the form x^2 + bx + c? that means you divide everything by the coefficient of x first

anonymous · Answer

hmm I see...

lgbasallote · Answer

tricky right ;)

anonymous · Answer

yes very... and I am stuck, haha

lgbasallote · Answer

you divide by 2 first that will give you x^2 - bx + 16 <--perfect square

anonymous · Answer

I don't divide b by 2?

lgbasallote · Answer

wait that should be x^2 - b/2 x +16 lol sorry

anonymous · Answer

Okay so b is 16

lgbasallote · Answer

yep

lgbasallote · Answer

you got it!

anonymous · Answer

cool... Thanks @lgbasallote

lgbasallote · Answer

$$\Huge \color{maroon}{\mathtt{\text{<tips hat>}}}$$

anonymous · Answer

Lol...[English accent] Why, Thank you fine sir...