f(x)=4x^2-x-3. If f(x)=-3, what is x?
I'm stuck on this problem. What do I do after 0=4x^2-x

Question

f(x)=4x^2-x-3. If f(x)=-3, what is x?
I'm stuck on this problem. What do I do after 0=4x^2-x

whpalmer4 · Answer

$$f(x) = 4x^2-x-3$$$$f(x) = -3$$$$4x^2-x-3=-3$$Add 3 to both sides$$4x^2-x=0$$Can you factor the left side?

anonymous · Answer

Yeah, the x.

anonymous · Answer

Or -x?

whpalmer4 · Answer

@mathslover I think they are trying to find the value of x that makes f(x) = -3, not evaluate f(-3)...

mathslover · Answer

Oops thanks for correction, I think i should delete my comment. Sorry @whpalmer4 for mistake and thanks a lot for correcting it.You may continue

anonymous · Answer

So do I factor out an x or -x?

whpalmer4 · Answer

You could factor out either one, of course.  You'll just have a different order to the stuff in the parentheses.
$$x(4x-1) = 0$$or$$-x(1-4x)=0$$You should be able to convince yourself that they are equivalent.

whpalmer4 · Answer

In either case, to have a product that equals 0, one or more of the things being multiplied must also equal 0.  Set them each equal to 0 and solve for the values of $x$ that make it true.

anonymous · Answer

Do I set it as x=0, 4x-1=0?