Question

use the quadratic formula to solve 4x^2+3x=8 round your answer to the nearest tenth

Answer 1

please I really need help!

Answer 2

do you know the quadraatic formula?

Answer 3

yes its x=-b \sqrt{b^2-4ac} all over 2a. my teacher didn't teach me what to do if theres a negative number in the square root sign. I really need help. i also keep forgetting the steps.

Answer 4

first thing is to write the quadratic equation as ax^2+bx+c=0,that is move the 8 to the left handside:
4x^2+3x-8=0

now a=4,b=3,c=-8

now compute b^2-4ac

Answer 5

it shouldn't be negative

Answer 6

yes it should be negative because you have to subtract the 8. 3+or- sqrt{9-119} all over 8

Answer 7

is that right?

Answer 8

you haven't calculated it yet?whats the answer??

Answer 9

sqrt{(3^2)-4(4)(-8)} = 11 something

Answer 10

sqrt {9 +128}

Answer 11

-3+or-sqrt{-119} all over 8. then i don't know what to do from here.

Answer 12

therefore +/- 1.08808...

Answer 13

inside your square root you have \[\sqrt{9-4(4)(-8)}\]
the negative before the 4ac and the negative on the -8 cancel out leaving 9 + 128 not 9-128 which is what you have calculated

Answer 14

oh ok I think i understand but can you still help me.

Answer 15

@martinez the roots aren't opposites of eachother

Answer 16

what now i am totally confused. please explain.

Answer 17

i told you to calculate b^2-4ac,do it first

Answer 18

-3+or-sqrt{-119} all over 8. then i don't know what to do from here. is that even right?

Answer 19

no more -119 it is -3 + or - sqrt{137} all over 8.
Since it is a quadratic with a + and - you will get 1.1 and -1.8

Answer 20

ok how did you do that?

Answer 21

\[-b \pm \sqrt{b ^{2}} -4(a)(c)\] all over 2a

Answer 22

so \[(-3\pm \sqrt{3^{2}-4(4)(-8)})/2(4)\]

Answer 23

(-3 + sqrt{137} ) / 8 && (-3 - sqrt{137} ) / 8

Answer 24

ok i see that. thank you very much you just really helped me.

Answer 25

also on your earlier question about what your teacher wants you to do for a negative number under the square root sign. At this moment nothing, but if you want to show off an answer (most likely a mistake) use i. i stands for a non real number \[\sqrt{-1}\] and -1 multiplied by anything negative becomes positive. Therefore adding i to any answer that has a negative under the square root makes the answer under the square root a positive times i.

Answer 26

ok so where would i put the i and the out side of the square root sign or the inside?

Answer 27

Anything I say from this point forward you should discredit as relevant to your homework until a trigonometry/ precalc/ calc class.
That being said: the form would go \[a \pm bi\]
where a and b are variables that have no relevance I just chose them as such
and where this particular equation would be \[(-3 \pm i \sqrt{137}) / 8\]

Answer 28

ok cool that helps a lot. thanks your wonderful.