Posted by **ladybug** on Friday, November 9, 2012 at 1:11pm.

Answer the following function.

f(x)=2x^2-x-1

A. Is the point (-2,9) on the graph of f?

B. If x equals 2, what is fx? What point(S) are on the graph of f?

c. if f(x)= -1, what is x? what point(s) are on the graph of f?

d. what is the domain of f?

e. List the x-intercpts, if any, of the graph of f.

f. List the y-intercept if any, of the graph of f.

**Can someone please help me with this. I have no idea, i'm lost!!!

- college algebra, Please help!! -
**Reiny**, Friday, November 9, 2012 at 3:22pm
Do you realize that

f(x) = 2x^2 - x - 1 and y = 2x^2 - x - 1 say the same thing ?

A) sub in the values x = -2 and y - 9 and see if they satisfy the equation

LS = 2(-2)^2 - (-2) - 1

= 8 + 2 + 1 = 9

RS = 9 = LS

Yes , the point (-2,9) does lie on the graph.

B) replace x with 2 and evaluate

C) f(x) = -1 is the same as saying y = -1

so 2x^2 - x - 1 = -1

2x^2 - x = 0

x(2x-1) = 0

x = 0 or x = 1/2

the two corresponding points are (0,-1) and (1/2, -1)

D) the domain of a function are the values of x that you may use in the equation. Can't we use any x we feel like ? , so the domain is the set of real numbers

E) at the x-intercept, y = 0

2x^2 - x - 1 = 0

(2x + 1)(x - 1) = 0

x = -1/2 or x = 1 -----> the two x-intercepts

F) for the y-intercept , let x = 0

y = 0 - 0 - 1 = -1

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