Question

f(x)=2x^2-x-1. If f(x)=-1, what is x?

Answer 1

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

Answer 2

solve for x

Answer 3

I tried to move the -1 over so that the equation would be \[2x^2-x-1+1=0\]

Answer 4

Now I'm at \[2x^2-x=0\] and I'm not sure what to do next

Answer 5

yes

so then:
-1 + 1 = 0

so:

\[2x^2 - x = 0\]

Answer 6

Oh, factor out an x?

Answer 7

yes

Answer 8

\[x(2x - 1) = 0\]

Answer 9

$$f(x)=-1\\2x^2-x-1=-1\\2x^2-x=0\\x(2x-1)=0\\x=0,2x-1=0\\x\in\left\{0,\frac12\right\}$$

Answer 10

Cool, those are the answers that I got. Thanks :)