Question

Let f(x) = ax³ - bx + 2 where a and b are constants. If f(4) = -5, then f(-4) = ?
A) 9
B) 5
C) 1
D) -1
E) -4

Answer 1

Do you have an idea about what the answer is?

Answer 2

No idea.

Answer 3

It just seems like there is not enough given information...

Answer 4

I am guessing that, because if f(4)= -5 that the f(-4)= (-5 x -1) Because 4 x -1 = -4

Answer 5

if that makes sense

Answer 6

But f(x) is neither even nor odd function...

Answer 7

It doesn't make sense to me.

Answer 8

I am just ignoring the first part..

Answer 9

@Mertsj Do you know if I am right?

Answer 10

plug in x = 4 and y = -5 to get one equation in terms of a and b

then plug in x = -4 to get another equation in terms of 'a' and b

then add the two equations

Answer 11

afterwards, solve for y

Answer 12

Huh? @jim_thompson5910

Answer 13

y = a*x^3-b*x+2

-5 = a*(4)^3-b*(4)+2

-5 = 64a - 4b + 2

-5 - 2 = 64a - 4b

64a - 4b = -7

Answer 14

y = a*x^3-b*x+2

y = a*(-4)^3-b*(-4)+2

y = -64a+4b+2

-64a + 4b + 2 = y

Answer 15

add the two equations

64a - 4b = -7
-64a + 4b + 2 = y
------------------
0a + 0b + 2 = -7 + y

which gives us

2 = -7 + y

Answer 16

Thanks!

Answer 17

Oh.