Question

The function f(x)=2x^3-4x+1 has the output value 12 for exactly one input value of x. Between which of the following pairs of numbers does this input value of x lie?

2.08 and 2.09
2.10 and 2.11
2.12 and 2.13
2.14 and 2.15
2.16 and 2.17
2.19 and 2.20
None of the above

Please explain. Thank you!

Answer 1

How do I do this do I plug the numbers in?

Answer 2

By plugging them in for x

Answer 3

So plug in for example 2(2.08)^3-4(2.08)+1=10.68 and then 2(2.09)^3-4(2.09)+1=10.89

Answer 4

Keep trying until you get close enough to the exact value.

Answer 5

for 2(2.14)^3-4(2.14)+1 I got 12.04 and 2(2.15)^3-4(2.15)+1 I got 12.28

Answer 6

Keep trying until you get close enough without going over.

Answer 7

and then for 2.16 and 2.17

I got 12.51 - 12.76

Answer 8

@hero so what would it be?

Answer 9

@hero or is it none of the above

Answer 10

Why'd you skip 2.09 thru 2.13

Answer 11

@hero I did those but those were closer to 12

2.08 and 2.09 = 10.68 - 10.89
2.10 and 2.11 = 11.12 - 11.81
2.12 and 2.13 = 11.58 - 11.81

Answer 12

Try 2.13-2.14

Answer 13

And that should let you know what the answer is

Answer 14

but that's not a choice

Answer 15

@hero 11.81 - 12.04 i seen someone mention online that "The easiest way to do this is probably to try each pair of numbers and see which one gives numbers on either side of 12." which is what we have been doing but what does it mean by either side of 12?

Answer 16

"above or below" 12

Answer 17

on a number line

Answer 18

above and below 12 would be all of them except 2.14 and 2.15 and 2.16 and 2.17

Answer 19

Not really.

Answer 20

@hero it doesn't look like none of them are the answer because 12 does not fall in between any of these numbers

Answer 21

Okay.