Question

How do I solve for x?
f(x) = 7 - 15x + 9x^2 - x^3
For the answer it says :
-x^2+8x-7=0
(-x+7)(x-1)=0
x=7 x=1
But how did they get to that?

Answer 1

You want to find the zero's? (x intercepts)

Answer 2

yes

Answer 3

Simply set f(x) for 0 and factor it, remember to put it in standard form though :>

f(x) = -x^3 + 9x^2 - 15x + 7

0 = -x^3 + 9x^2 - 15x + 7

Now try to factor it :>

Answer 4

that's what i don't understand. how would you factor that?

Answer 5

Factor it by grouping :o

Take the first two terms and factor that, then take the last two terms and factor those :>

The neat thing is that when you factor it, you should get the same value inside the parenthesis cx

Answer 6

so -x^3+9x^2 would be -x^2(x-9)?
and how would I factor -15x+7?

Answer 7

you can't factor it like that, and solve it using just alg 1 for this.

Do you know what the possible zeros are? Check them...

Answer 8

Hm, well,

-1((x-1)^2(x-7)) = 0, if you multiply both sides by -1 you would get (x-1)^2(x-7) = 0

(x-1)^2 = 0

√(x-1)^2 = 0
x - 1 = 0
+1 +1

x = 1

(x-7) = 0
+7 + 7

x = 7

So you have x = {1,7}, I meant to regroup them in my last reply x.x

Answer 9

Here, see if this helps; http://www.sparknotes.com/math/algebra2/polynomials/section4.rhtml

Answer 10

alright..i'm trying to understand this.

Answer 11

Have fun cx

Answer 12

for the explanation of the answer, it says
-x^2+8x-7=0
(-x+7)(x-1)=0
x=7 x=1
How did they get -x^2+8x-7=0

Answer 13

Hint: p/q and synthetic division

Answer 14

ohh ok. Thank you!

Answer 15

Yw xD