Question

Is this correct, and if not where is the mistake?

21x^2 - 46x + 15

Factors of 21:
3 x 7

Factors of 15:
3 x 5

3 x 3 + 7 x 5 = 9 + 35 = 46

Since it has to be -46 and + 15, then the factors of 15 are both negative.

Factored: (7x - 3)(3x - 5)

Answer 1

Medal given!

Answer 2

It gives after expanding 21x²-44x+15 :(

Answer 3

Look at the mess WolframAlpha makes of it:
http://www.wolframalpha.com/input/?i=factor+21x^2+-+46x+%2B+15

Seems there is an error in the thing.

Answer 4

There is a mistake in the expression itself? So 21x^2 - 46x + 15 can't be factored?

Answer 5

That's what I tried to say!

Answer 6

9+35=44 not 46

Answer 7

Nice one ingenuus, I didn't notice it. Do you have any solution for that?

Answer 8

There is no solution for it.
If the expression was 21x² - 44x + 15, everything would be fine.

Answer 9

So isn't there another way/method for it to be factored?

Answer 10

Take a look at the WolframAlpha solution...

Answer 11

x-(23+\[21(x -(23+\sqrt{214})/21)(x-(23-\sqrt{214})/21)\])

Answer 12

only the midde one is the answer..

Answer 13

you couldn't have guessed that one could you :)

Answer 14

the test shows it has 2 solutions, so it can be factorized.
use the formula to figure it out.

Answer 15

unfortunatly some irrational number will pop out

Answer 16

So if I expand 21(x−(23+214−−−√)/21)(x−(23−214−−−√)/21) it's going to give me: 21x^2 - 46x + 15 ?

Answer 17

or?

Answer 18

why don't you try out yourself.
i think that will be more helpful to you

Answer 19

i just tried it and it works like magic :)

Answer 20

you know, every ax^2+bx+c can be factorized if we allow complex numbers.

Answer 21

anyways, i think you got my point right on the method of factorizing. good luck!

Answer 22

So I will try to expand 21(x−(23+214−−−√)/21)(x−(23−214−−−√)/21) and try to get my result right?

Answer 23

yeah it will get you right
you know \[(a+b)(a-b)=a^2-b^2\] right?
it will help you expand

Answer 24

So with my way it can't be solved I take it