Question

Solve. 3x2 = -15x + 21

Answer 1

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Answer 2

So i know what to do up until the point where my answer looks like 3x^2-15x-21=0

Answer 3

You need to add 21 to both sides

Answer 4

then what?
is it supposed to look like 3x^2-15x=21?

Answer 5

Yes. Now, 3x^2 is
9x-15x=21
^^^^^^
Combine
-6x = 21
--- ---
-6 -6
x = ??

Answer 6

-3.5

Answer 7

what is that in a square root form?

Answer 8

Errr.... idk right off

Answer 9

well my answer options are
A. the quantity of negative 5 plus or minus i square root 3 all over 2
B. the quantity of 5 plus or minus square root 53 all over 2
C. the quantity of 5 plus or minus 3 square root 3 all over 2
D. the quantity of negative 5 plus or minus square root 53 all over 2

Answer 10

Errrr.....

Answer 11

im stuck on it too

Answer 12

@agent0smith ??

Answer 13

3x^2-15x-21=0

From here, you can take out a common factor of 3.

Answer 14

ok so 3(x-5x-7)=0

Answer 15

I dont know what to do nexst because this trinomial can't be changed

Answer 16

You forgot the x^2

3(x^2-5x-7)=0

Now divide both sides by 3.

You can't factor it, use the quadratic formula.

Answer 17

then I get 5+_ sqrt 109 over 6

Answer 18

Keep in mind that you are using the quadratic formula for x^2-5x-7=0... it looks like you didn't do it for that.

Answer 19

How do I do it for that then?

Answer 20

By using the quadratic formula. It looks you used 3(x^2-5x-7)=0 and not x^2-5x-7=0... meaning you did not divide both sides by 3.

Answer 21

oh ok
-5/3x-7/3=0
is this right?

Answer 22

3(x^2-5x-7)=0

When you divide both sides by 3, you do not touch anything inside the parentheses.

Answer 23

so it is like i said before x^2-5x-7=0 or not?

Answer 24

Yes. Now use the quadratic formula.

Answer 25

which is what I used before?

Answer 26

Then how did you get the "over 6" part? The denominator of the quadratic formula is 2a.

Answer 27

oh ok. I see so it is
(5+-√53)/2

Thank you so much!

Answer 28

He's very smart(:

Answer 29

Much better.

And ty!