Question

Solve this quadratic equation using the quadratic formula. x^2 + 8x - 5 = 0

Answer 1

@phi

Answer 2

do you know the quadratic formula?

Answer 3

0.58257569495584, -8.58257569495584.

Answer 4

ya \[-b \pm \sqrt{b ^{2}-4ac}\]

Answer 5

i gave u the answer

Answer 6

ya but I need to know how to do it

Answer 7

If you are fuzzy on using it, watch this when you have time
http://www.khanacademy.org/math/algebra/quadratics/quadratic_formula/v/using-the-quadratic-formula

meanwhile, you want to match the letters a, b and c to your problem

Answer 8

I KNOW

Answer 9

x^2 + 8x - 5 = 0

you "pattern match" that to
a x^2 + b x + c=0

what do you get for a, b and c ?

Answer 10

btw, we want to divide by 2a in the formula
\[ (-b \pm \sqrt{b ^{2}-4ac})/2a \]

Answer 11

First step is give the numbers for a,b and c
can you do that ?

Answer 12

A=1
B=8
C=-5

Answer 13

Am I right

Answer 14

@ProfessorMath can u help me

Answer 15

@Callisto will u hel me

Answer 16

a=1, b=8, c=-5
Correct.
Now substitute these values into the quadratic formula
\[x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}\]to find x.

Answer 17

\[-8\pm \sqrt{8^{2}-4*1*-5}\]

Answer 18

No.. You need the denominator (2a) too!

Answer 19

\[-8\pm \sqrt{84-4*1*5}\div2*1\]

Answer 20

\[-8\pm \sqrt{80*1*5\div2}\]

Answer 21

8^2 = 64
\[x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}=\frac{-8\pm \sqrt{8^2-4(1)(-5)}}{2(1)}=\frac{-8\pm \sqrt{64-4(1)(-5)}}{2(1)}=...?\]

Answer 22

ya I get stuck after this

Answer 23

Simplify the value under the square root first.
What is
64 - 4(1)(-5)?

Answer 24

84

Answer 25

Can one of yal help me

Answer 26

Yes. So, now, we get
\[x=\frac{-8\pm \sqrt{84}}{2(1)}\]
84 = (2^2)x3x7, so
\[x=\frac{-8\pm \sqrt{2^2\times 3\times 7}}{2(1)}=\frac{-8\pm 2\sqrt{3\times 7}}{2(1)}\]Can you simplify it?

Answer 27

they both equal 84

Answer 28

Hmm... they =?

Answer 29

idk im getting confused

Answer 30

Confused at?

Answer 31

I have to find what X=

Answer 32

That's what we have been working on.

Answer 33

o wow this takes a long time

Answer 34

so I go t
\[x=-8\pm \sqrt{84} \div2\]

Answer 35

\[x=(-8\pm \sqrt{84})\div2\]

Answer 36

ya wats next

Answer 37

Simplify it.

Answer 38

okay so its
\[-8\pm9.16515\div2\]

Answer 39

is that right

Answer 40

\[-8\pm4.58258\]
this is after I div 9.16515 by 2

Answer 41

\[(-8\pm 9.16515)\div2\]Add/subtract before you divide.

Answer 42

the \[-8+9.16515 \div2=0.58258\] that's add
the \[-8-9.16515\div2=-8.58258\] that's subtract

Answer 43

Is that right @Callisto

Answer 44

Yes. But remember to put brackets for the addition/subtraction part.

Answer 45

what would x=