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What is f(x)?

I dont understand how to solve quadratic functions. I'm supposed to solve f(x)-x^2+2x-3 by completing the square  but whenever I try to search how to do these kind of problems, I never see a problem with f(x) !!! Please help me D: 

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Maxine M. | Here to help you rediscover mathHere to help you rediscover math
5.0 5.0 (13 lesson ratings) (13)

I was also wondering if you had written this correctly? Just as John R. said; f(x) is the "function of x" which I frequently just say f(x)=y.

John R. | Physics and Math Tutor – Kind, Easy-going, PatientPhysics and Math Tutor – Kind, Easy-goin...
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f(x) is a notation for a "function of x." Usually it is written as f(x)= "something", which is an expression with x as what we call the independent variable. Many times f(x) and y are the same thing. In solving a quadratic equation you are looking for the roots of the expression in the form of a^2 + bx + c. And the roots are defined as the values where this expression equal zero (on a graph, it's where the curve crosses the x-axis). So what you are looking for is the values of x that satisfy x^2 + 2x - 3 = 0. (I'm guessing your teacher means f(x) = x^2 + 2x - 3) To start focus on the portion of this expression x^2 + 2x. Now ask yourself if you can find a number that when added to this will allow you to write it as a quantity squared i.e (x + k)^2. So we want (x + k)^2 which is the same as x^2 + 2xk + k^2 = x^2 + 2x. It looks like k = 1. So if we go back to the original equation, x^2 + 2x - 3 = 0. If we add k^2, that is 1, to both sides we get x^2 + 2x + 1 - 3 = 1. Now make the simplification you just determined: (x + 1)^2 - 3 = 1. (You just completed the square). Rearranging: (x - 1)^2 = 4. Can you solve this from here? Be sure to check your answers (there are two of them) by substituting them, one at a time, back into the original equation. The next topic you are likely to study is the quadratic equation. It is based on this method.
Dalila G. | I could tutor for every subject! All we need is your textbook :)I could tutor for every subject! All we ...

Hey there, well for starters f(x) is basically like saying Y.. ( ex: y=x+2 so this would be like f(x)=x+2 ) therefore you might have written the problem incorrectly because f(x) should be equal to something, ex f(x)=x^2+2x-3 that would be your function.