Question

Is this right ?
(2x-8)(2x+1)=x^2-16
2(x-4)(2x+1)=(x-4)(x+4) l /x-4
2(2x+1)=x+4 l -x+4
4x+2-x+4=0
3x+6=0 l -6
3x=-6 l /3
x=-2

Answer 1

Yes .-.

Answer 2

seems unlikely but maybe

Answer 3

Following me around again @satellite73

Answer 4

I got the same answer , lemme see if i can get a different answer by doing it right ..

Answer 5

no it is not right

Answer 6

@Hero yeah, i need to keep you honest!

Answer 7

Here's how to figure out if you ever doubt yourself , take your number you get for x which in your case you got -2 , & simply substitute it for x ..
so it should be
(2)(-2)-8(2)(-2)+1 = -2 squared - 16

Answer 8

I was hoping I would be able to travel to and fro without having to watch my back.

Answer 9

What is it then ?

Answer 10

The first problem is here:

2(x-4)(2x+1)=(x-4)(x+4) l /x-4

You can divide by x-4, if you don't know that x-4 is not=0.

Answer 11

Use quad formula, complete the square or whatever method you feel comfortable with to isolate x.

Answer 12

oops

Answer 13

Compounded here:

2(2x+1)=x+4 l -x+4
4x+2-x+4=0

IF the step before were correct, you would subtract (x+4), not subtract x and add 4.

Answer 14

\(4x^2-x^2=?\)

Answer 15

*You CAN'T divide by x-4, if you don't know that x-4 is not=0.

Answer 16

@Hero did i make you nervous or something?

Answer 17

No, you didn't, I just goofed.

Answer 18

(2x−8)(2x+1)=x^2−16


Multiply the right side:
2x(2x+1)−8(2x+1)=x^2−16
4x^2+2x−16x−8=x^2−16
4x^2−14x−8=x^2−16


Subtract x^2 from both sides:
3x^2−14x−8=−16


Add 16 to both sides:
3x^2−14x+8=0

Answer 19

Now, you can use quad formula, or complete the square, or whatever method feels comfortable for you.

Answer 20

I need to know what x is.

Answer 21

Do you know any methods to isolate x such as factoring, quadratic formula or complete the square?

Answer 22

I know methods to facrorise.

Answer 23

Well, believe it or not

3x^2 -14x + 8 = 0

Is factorable

Answer 24

a^2-2ab+b^2=(a-b)^2 ?

Answer 25

That only works if you have a perfect square.

Answer 26

Yes.

Answer 27

3x^2 - 14x + 8 = 0

that's not a perfect square, but it is factorable. Try finding two numbers that multiply to get 24 yet add to get -14

m x n = 24
m + n = -14

Answer 28

12 and 2.

Answer 29

Actually

-12 and -2

Answer 30

Yes.

Answer 31

We can replace -14 with -(12 + 2) in the equation:

3x^2 - (12 + 2)x + 8 = 0
3x^2 -12x - 2x + 8 = 0

Answer 32

Now we can factor by grouping.

Answer 33

If you factor the first two terms you get 3x(x - 4)
If you factor the last two terms you gete -2(x - 4)

So you have
3x(x - 4) - 2(x - 4) = 0
x - 4 is also common to both so you factor that out to get
(x - 4)(3x - 2) = 0

From here, you use zero product property:

x - 4 = 0
3x - 2 = 0

So there are two values of x