Question

For the form of the equation ax^2+bx+c=0 you know c (-7.2) and both answers x1 = -2 x2 = 4 what are then a and b?

Answer 1

@ash2326 @Callisto @dmac83 @experimentX

Answer 2

@jhonyy9

Answer 3

@sarahusher @kirad @LostInSchool

Answer 4

@whambamsham @worldcoin @eliassaab @robtobey @RANE

Answer 5

@Triton

Answer 6

@theycallmerhea

Answer 7

@Orion1213

Answer 8

@phi

Answer 9

Does anybody think they can help?

Answer 10

Try this (as step 1):
in your equation
\[ ax^2+bx+c=0 \]
replace c with -7.2 and x with -2 and simplify as much as possible
what do you get ?

Answer 11

Nooo that's not what I meant sorry.

Answer 12

x1 and x2 are the answers...

Answer 13

Oh, lol yeah I get what you said now lol

Answer 14

But that's not how we're supposed to solve it.

Answer 15

usually we solve for "x". (and we know a,b, and c)
but in this case, we are going to solve for a and b, (but we know x)

so replace c with -7.2 and x with -2 and simplify as much as possible what do you get ?

Answer 16

Okay just a minute.

Answer 17

4a + -2b - 7.2 = 0

Answer 18

looks good.

now do the same thing, but use x= 4
we will get another equation

Answer 19

Okay...
16a + 4b - 7.2 = 0

Answer 20

yes, now we have 2 equations and 2 unknowns. There are ways to solve these things.
16a + 4b - 7.2 = 0
4a + -2b - 7.2 = 0

one way is multiply the bottom equation by 2 (that means both sides all terms)
then add this "new" equation to the first equation.

Answer 21

Maybe, but I'm sorry cause we didn't learn ANY of this.. we did the thing with Vieta though, and I'm pretty sure that's how we should solve this.

Answer 22

Do you know what I'm talking about?

Answer 23

Yes, you can do it that way.
x1 + x2 = -b/a
x1 * x2= c/a

I would use the 2nd equation first, to solve for a.
can you do that ?

Answer 24

Okay, that's what I thought, thanks!

Answer 25

Wait, so what is -b/a exactly?

Answer 26

a , b and c are the coefficients in front of
a x^2 + bx + c = 0

you need to find a and b

in the 2nd equation
x1 * x2 = c/a
they give you x1 and x2 and c
that leaves a the only unknown.

replace the letters with the numbers they gave you, and simplify
what do you get ?

Answer 27

Yeah I know, but how will knowing -b/a help me??

Answer 28

It will be clear in a moment.
First, do
x1 * x2 = c/a

Answer 29

Okay, -2 times 4 is -8

Answer 30

And since c is 7.2

Answer 31

be careful, c= -7.2

Answer 32

a is .9

Answer 33

Okay, it sucks cause I did exactly this, I just made a calculating error before lol But thanks a lot! :D I can do the rest by myself!!

Answer 34

yes, a is 0.9

now that you know a, the first equation
x1+x2 = -b/a
has only *1 unknown*, the "b", so we can solve for it