Question

Help please?
Solve 2x2 - 8x = -7

Answer 1

So first move all terms to one side

Answer 2

Yes, like i did with the last equation, do I have to put this one into the quadratic formula or no?

Answer 3

Yes you do

Answer 4

I did that but I think i did it wrong because I didn't get any of the choices

Answer 5

negative 2 plus or minus square root of 2
negative 2 plus or minus 2 square root of 2
quantity of 2 plus or minus square root of 2 all over 2
2 plus or minus square root of 2 end root over 2

Answer 6

start with
\[ 2x^2 - 8x = -7 \]
add +7 to both sides, and you get
\[ 2x^2 - 8x +7=0 \]

what are "a", "b" and "c" for this equation?
in other words, match up your equation with
\[ ax^2 +bx+c= 0 \]

Answer 7

If you want more info, maybe this helps
https://www.khanacademy.org/math/algebra/quadratics/quadratic-formula/v/using-the-quadratic-formula

Answer 8

I know how to do the beginning to this equation but once I get to the solving it in the quadratic formula I get messed up, @phi

Answer 9

@kidrah69 help?

Answer 10

Have you figured out what your
a b and c value is?

Answer 11

a, 2 b, -8 c, -7

Answer 12

\[\frac{ x = -b ± \sqrt(b^2 - 4ac) }{ 2a }\]
good now plug it in

Answer 13

When I plug all that in i get -8 plus or minus the srqrt of -8^2 - 4(2)(-7) all over 2(2)

Answer 14

\[\sqrt{(-8)^2 - 4(2)(-7)}\]
solve

Answer 15

64-56 =8/4

Answer 16

no just solve whats in the square root dont square root it :P

Answer 17

what do you mean? if i take the -8^2 it will be 64 and then 4 times the 2 and the -7 would be 56 which equals 8?

Answer 18

hmmm we are not doing something right.....

Answer 19

I'm confused?

Answer 20

Well one problem it instead of a -7 there should be just a 7

Answer 21

ahh you're right cause we added it to the other side

Answer 22

We still get 8 though :/

Answer 23

yeah that's my problem, and the answer choices don't add up with my math

Answer 24

negative 2 plus or minus square root of 2
negative 2 plus or minus 2 square root of 2
quantity of 2 plus or minus square root of 2 all over 2
2 plus or minus square root of 2 end root over 2

Answer 25

2x2 - 8x = -7
Quadratic Formula:
\(x=\dfrac{8\pm\sqrt{4^2-4(2)(7)}}{2(2)}\)

\(x=\dfrac{8\pm\sqrt{16-56}}{4}\)

\(x=\dfrac{8\pm\sqrt{40}}{4}\)

Answer 26

But that still isn't any of the choices. It's okay don't stress this one, could you help me with something else?

Answer 27

Wat is the topic of the other one?

Answer 28

Same thing, I just want to know sometimes the answer have the same thing but one will be positive and the other answer negative (still dealing with quadratic formula) how do I know if its pos or neg?

Answer 29

Is this solving the formula? or do u mean with the abc values

Answer 30

I think part of the formula.. look

quantity of negative 9 plus or minus 3 square root of 5 all over 2
quantity of 9 plus or minus 3 square root of 5 all over 2

see how their the same answer but one is a negative 9 and the other a positive? How do I know which one is correct?

Answer 31

@kidrah69, do you get what I'm saying?

Answer 32

Well when you do the work it before the squrt is has -9 it will be a negative number if not assume its postivie

Answer 33

Okay, thanks for you help! I appreciate it :-)

Answer 34

:)
http://www.purplemath.com/modules/quadform.htm
http://www.mathsisfun.com/definitions/quadratic-equation.html
This should help too

Answer 35

thank you soo mcuh!

Answer 36

:)

Answer 37

\[ 2x^2 - 8x +7=0 \]
a=2 , b= -8, c=7
now do things slowly and carefully
\[ b^2 -4 ac= (-8)^2 - 4\cdot 2 \cdot 7= 64 - 56 = 8\]
\[ \sqrt{ b^2 -4 ac}= \sqrt{8} \\= \sqrt{4\cdot 2} \\= \sqrt{4} \sqrt{2} \\= 2 \sqrt{2}\]


so we the answers are
\[ \frac{-b \pm \sqrt{ b^2 -4 ac}}{2a} \\= \frac{-(-8) \pm 2 \sqrt{2}}{2\cdot 2} \]
you can simplify that to
\[ \frac{8 \pm 2 \sqrt{2}}{2\cdot 2} = 2 \pm \frac{\sqrt{2}}{2}\]

Answer 38

Thank you so much @phi! :)