OpenStudy (srtauser):

Solve. 3x2 = -15x + 21

2 years ago
OpenStudy (soprano.h.d0816):

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2 years ago
OpenStudy (srtauser):

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

2 years ago
OpenStudy (soprano.h.d0816):

You need to add 21 to both sides

2 years ago
OpenStudy (srtauser):

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

2 years ago
OpenStudy (soprano.h.d0816):

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

2 years ago
OpenStudy (srtauser):

-3.5

2 years ago
OpenStudy (srtauser):

what is that in a square root form?

2 years ago
OpenStudy (soprano.h.d0816):

Errr.... idk right off

2 years ago
OpenStudy (srtauser):

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

2 years ago
OpenStudy (soprano.h.d0816):

Errrr.....

2 years ago
OpenStudy (srtauser):

im stuck on it too

2 years ago
OpenStudy (soprano.h.d0816):

@agent0smith ??

2 years ago
OpenStudy (agent0smith):

3x^2-15x-21=0 From here, you can take out a common factor of 3.

2 years ago
OpenStudy (srtauser):

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

2 years ago
OpenStudy (srtauser):

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

2 years ago
OpenStudy (agent0smith):

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.

2 years ago
OpenStudy (srtauser):

then I get 5+_ sqrt 109 over 6

2 years ago
OpenStudy (agent0smith):

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.

2 years ago
OpenStudy (srtauser):

How do I do it for that then?

2 years ago
OpenStudy (agent0smith):

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.

2 years ago
OpenStudy (srtauser):

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

2 years ago
OpenStudy (agent0smith):

3(x^2-5x-7)=0 When you divide both sides by 3, you do not touch anything inside the parentheses.

2 years ago
OpenStudy (srtauser):

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

2 years ago
OpenStudy (agent0smith):

Yes. Now use the quadratic formula.

2 years ago
OpenStudy (srtauser):

which is what I used before?

2 years ago
OpenStudy (agent0smith):

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

2 years ago
OpenStudy (srtauser):

oh ok. I see so it is (5+-√53)/2 Thank you so much!

2 years ago
OpenStudy (soprano.h.d0816):

He's very smart(:

2 years ago
OpenStudy (agent0smith):

Much better. And ty!

2 years ago