Please help with a Quadratic homework problem.

Write the quadratic equation whose roots are 5 and - 4, and whose leading coefficient is 2. (Use the letter x to represent the variable).

____ = 0

Question

Please help with a Quadratic homework problem.

Write the quadratic equation whose roots are 5 and - 4, and whose leading coefficient is 2. (Use the letter x to represent the variable).

____ = 0

luigi0210 · Answer

Work backwards

anonymous · Answer

here i will get you started :) $$c(x - r)(x - r)$$ the c is the coefficient while the r is the root plug in the numbers and tell me what you get :)

anonymous · Answer

$$c(x - r_{1})(x-r_{2})$$ just to show that you have to use both roots

anonymous · Answer

I multiplied the coefficient 2 by both roots but is unsure of my answer: 2^2-8-40=0

anonymous · Answer

is that -8x?

anonymous · Answer

Yes.

anonymous · Answer

i got something different :O you mind if i show you step by step and see if you can find mine or yours error?

anonymous · Answer

Please show me the step by step!

anonymous · Answer

well you should have setup the problem like this :
$$2(x-5)(x+4)$$ did you setup correctly?

anonymous · Answer

Yes, that is how my equation looks.

anonymous · Answer

Actually, no, mine was 2(x-5) (x-4) this was the example in my math lab.

anonymous · Answer

they gave that to you as a example? :( but it calls for a -4?

luigi0210 · Answer

That's kind of right in a sense

anonymous · Answer

hmmmm!

anonymous · Answer

@Luigi0210 can you explain :) because now im confused on it

luigi0210 · Answer

But yea, it needs a -4.

luigi0210 · Answer

x=5
x=-4
Think of it this way. 
Ignore the coefficient for now

luigi0210 · Answer

Now work backwards. Subtract 5 from both sides and add 4 to both:
x-5=5-5
------------------
x+4=-4+4

Giving you:
(x-5)(x+4)

luigi0210 · Answer

*=0

anonymous · Answer

so is are we wrong or did she get the wrong example?

luigi0210 · Answer

(x-5)(x+4)=0
Now distribute this out

anonymous · Answer

because if she used (x-5)(x-4) we know what her problem is already

luigi0210 · Answer

The example must be wrong.

anonymous · Answer

The example shows different numbers and neither of them are negative.

anonymous · Answer

did you give us the wrong numbers ?

luigi0210 · Answer

The answer should be:
2x^2-2x-40

anonymous · Answer

yea what i got :)

anonymous · Answer

Ok, I was close but no cigar!  Thank you guys and Luidi here is your medal.

luigi0210 · Answer

Luidi? >.>

luigi0210 · Answer

You're Welcome.

anonymous · Answer

You guys are great!  Thank you!