Find a value of k such that 1/2 is a root of 2x^2+11x =-k
how do i do this?

Question

Find a value of k such that 1/2 is a root of 2x^2+11x =-k
how do i do this?

anonymous · Answer

Can you find the roots of quadratic equation by Quadratic Formula?

anonymous · Answer

Firstly add k to both the sides..

superhelp101 · Answer

yes i can

superhelp101 · Answer

can you find the roots of quadratic equation by Quadratic Formula?
i think i can do that

superhelp101 · Answer

2x^2+11x+k

anonymous · Answer

Just go with that..

superhelp101 · Answer

go with what lol?

anonymous · Answer

Go with that means go with the quadratic formula, use it and find the roots, do upto that..

superhelp101 · Answer

umm i am kinda confused. but thank you 
here maybe @iambatman can help?

anonymous · Answer

Who will write "=0" with that?? Note it..

superhelp101 · Answer

ok

anonymous · Answer

Trying to avoid calculations so that Batman can do that for you?? Clever..!!

superhelp101 · Answer

why??

superhelp101 · Answer

huh?

superhelp101 · Answer

ohh no!

superhelp101 · Answer

of course not! i want to know how to do the problem! that is why i said "how do i do this?" on my question

anonymous · Answer

But in comments you are avoiding to do that.. :P

superhelp101 · Answer

thats because i am really confused! :P

anonymous · Answer

I said to just start it by quadratic formula, just do it, if you are wrong, we will sort out that..

anonymous · Answer

If you are confused, then you must be confused somewhere, at some place, tell me that place buddy.. :P

superhelp101 · Answer

but, but is this the quadratic formula that you mean??? 2x^2+11x+k

superhelp101 · Answer

that is were i am confused :/
quadratic formula

anonymous · Answer

Leave it.. I tell from the beginning..

superhelp101 · Answer

ok!

anonymous · Answer

Firstly you will add k both the sides, because, the general quadratic equation is : $ax^2 + bx + c = 0$, this "=0" form in right side you have to achieve..

You can get that by adding k both the sides..

So, you will come to : $2x^2 + 11 + k = 0$
Right?

superhelp101 · Answer

yep!!!

anonymous · Answer

Now, using quadratic formula, :

$$x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$$

anonymous · Answer

can you tell what is a, b and c here by comparing with the given equation??

superhelp101 · Answer

yeah i can i see what you are doing you are factoring

anonymous · Answer

It is a kind of factoring, but in actual I am finding out values of x..

superhelp101 · Answer

oh right

anonymous · Answer

So, here you will get values of x as:

$$x = \frac{-11 \pm \sqrt{121 - 8k}}{4}$$

anonymous · Answer

Here, a = 2, b = 11 and c = k

superhelp101 · Answer

yes i understand that! :)

anonymous · Answer

Look you have got + and - sign in between, so for one root, you can take anyone.. Suppose I am taking -ve sign:
So I have:
$\large x = \frac{-11 - \sqrt{121 - 8k}}{4}$

anonymous · Answer

And you are given with that one root is 1/2, so just equate them:

$$\frac{-11 - \sqrt{121 - 8k}}{4} = \frac{1}{2}$$

anonymous · Answer

Now, you need to just solve it for $k$..

superhelp101 · Answer

but how do i do that?

anonymous · Answer

Multiply by 4 firstly both the sides..

Then, Add 11 both the sides..

Do this and show me where you reach..

superhelp101 · Answer

omg can't i just plug in 1/2 into the equation to get k???

anonymous · Answer

Yes, you can very well do that... :)

superhelp101 · Answer

yayay! but anyway thank you so much for taking you time for me to understand this concept!! :D

anonymous · Answer

So, what you got for k by doing that?

superhelp101 · Answer

-6