Fx = x to the 3 power +2x squared = 2x -9;?

Question

find f(-1), f(90), and f(2)

Answer 1

You have too many equal signs in your original question. F(x) is a function.

If f(x) = 2x^3 +3x -1 for example...

then f(2) = 2(2)^3 +3(2) -1
f(2) = 16 + 6 -1
f(2) = 21

Just substitute the value in the brackets for the variable x to find you answer

Answer 2

You can't have two "equal" signs. Please check your book to type the problem correctly. Do you mean f(x) = x^3 + 2x^2 - 2x - 9
Or, f(x) = x^3 + 2x^2 + 2x - 9? I'll solve both functions.

1. f(x) = x^3 + 2x^2 - 2x - 9
First: the problem gives you the values to place in the function...
Sec: replace each value with the x-variable in the function...

a) f(-1) = (-1)^3 + 2(-1)^2 - 2(-1) - 9
f(-1) = -1+ 2(1) + 2 - 9
f(-1) = -1 + 2 + 2 - 9
f(-1) = - 6

b) f(90) = (90)^3 + 2(90)^2 - 2(90) - 9
f(90) = (90)^3 + 2(90)^2 - 2(90) - 9
f(90) = 729,000 + 2(8,100) - 180 - 9
f(90) = 729,000 + 16,200 - 180 - 9
f(90) = 745,011

c) f(2) = 2^3 + 2(2)^2 - 2(2) - 9
f(2) = 8 + 2(4) - 4 - 9
f(2) = 8 + 8 - 4 - 9
f(2) = 3

2. f(x) = x^3 + 2x^2 + 2x - 9

a) f(-1) = (-1)^3 + 2(-1)^2 + 2(-1) - 9
f(-1) = -1 + 2(1) - 2 - 9
f(-1) = -1 + 2 - 2 - 9
f(-1) = 8

b) f(90) = (90)^3 + 2(90)^2 + 2(90) - 9
f(90) = (90)^3 + 2(90)^2 + 2(90) - 9
f(90) = 729,000 + 2(8,100) + 180 - 9
f(90) = 729,000 + 2(8,100) + 180 - 9
f(90) = 729,000 + 16,200 + 180 - 9
f(90) = 74,5371

c) f(2) = 2^3 + 2(2)^2 + 2(2) - 9
f(2) = 8 + 2(4) + 4 - 9
f(2) = 8 + 8 + 4 - 9
f(2) = 11

Answer 3

f(x)= x^3+2x^2 = 2x-9

manipulate the equation first:
x^3 + 2x^2 - 2x + 9

so f(x) = x^3 + 2x^2 - 2x + 9

Then, to find f(90), substitute the x in the equation with 90.
Likewise, to find f(2), substitute the x with 2.
Do the same for the other (-1).