math7


taw
Member
Registered: 23.04.17 23:58
Timezone: UTC +0
Posts: 1

What's the format of the answer?

It's a very simple question, but it just won't accept answer which
I know to be correct in any format I tried.


ynori7
Administrator
Registered: 24.08.11 12:16
Timezone: UTC +2
Posts: 143

It should be an integer.

i537.photobucket.com/albums/ff338/ynori77/archenemysig1.jpg


taw
Member
Registered: 23.04.17 23:58
Timezone: UTC +0
Posts: 1

ynori7 wrote:
It should be an integer.

f(x) = ax^2 + 12x + 1
Given that the maximum value of the curve generated by the above equation is f(x)=7, what is the value of a?

There are no integer values of a for which this function maxes out at x=7, even if we restrict it to integer xs.

For real numbers, that a is a fraction (and f(7) is then integer, but that doesn't get accepted either).


ynori7
Administrator
Registered: 24.08.11 12:16
Timezone: UTC +2
Posts: 143

taw wrote:
There are no integer values of a for which this function maxes out at x=7, even if we restrict it to integer xs.

False. There is an integer value which produced a max (y=7) at some x value (let's call that value of x "b" ). Not only is b an integer too, but the values of y at b+1 and b-1 are also integers.

Try using some basic calculus to produce a second equation. Then you'll have two equations and two unknowns (a and x).

i537.photobucket.com/albums/ff338/ynori77/archenemysig1.jpg