Question

Please Help!
What are the x-intercepts of y = 2(x - 4)(x + 1)

Answer 1

let y=0
ans solve for x

Answer 2

(0,-4)
that should be your answer

Answer 3

@weasle the function in question is a parabola which crosses the x-axis twice. You're trying to find the values of \(x\) where that happens.

Answer 4

@weasle its not one of the choices

Answer 5

hold on

Answer 6

\[0 = 2(x-4)(x+1)\]Your job is to find the values of \(x\) that make that statement true. You should be able to do this just by thinking a little bit.

Answer 7

If you have \[a*b = 0\]what must be true about a and b?

Answer 8

One of them has to be 0, right?

Answer 9

its -1 and 4 thank you all for trying to help

Answer 10

Don't go, you're not done yet.

Answer 11

@whpalmer4 ok what else needs to be done?

Answer 12

You need to understand how to get the answer :-)

So the only way we can get \[0 = 2(x-4)(x+1)\] is if \[x-4=0\]or \[x+1=0\]If you solve those two equations, you'll get the answer values.

Usually, you'll be given an equation that isn't already factored, and then finding the solutions is not as easy. For example, it's obvious that you can look at this one and say "x = 4, x = -1" but if they gave us the equation multiplied out, wouldn't be so easy to see that for \[2x^2-6x-8=0\]you get the same answers, would it?

Answer 13

But you do:

\[2(4)^2-6(4)-8 = 0\]\[2*16-24-8 = 0\]\[32-24-8=0\]\[0=0\]

and
\[2(-1)^2-6(-1)-8=0\]\[2(1)+6-8 = 0\]\[2+6-8=0\]\[0=0\]

Answer 14

You'll be seeing a lot of this concept, trust me :-)

Answer 15

@whpalmer4 Thank you so much for teaching me how to check my answers :)

Answer 16

sorry for not being able to help more. :(

Answer 17

@weasle Its ok thank you for trying :)

Answer 18

I figure if the problem is worth doing, you might as well make sure you've got the right answer :-)

Answer 19

@whpalmer4 Thank you!

Answer 20

Here's a graph of that function, by the way. You can clearly see the solutions are the points where the parabola crosses the x axis.