I'm a little confused as using the quadratic formula would leave me with and , but does not equal the original function.
Multiplying out will give you and if you multiply this by a factor of -4.9 you get the original f(x) you had.
You could also do this the other way, you are looking for roots to the equation f(x)=0 so you get . Divide through by 4.9 and you get the equation I gave above.
If we assume that f(x)=0
Then we assume that:
My times table is a little rusty, so allow me to tidy this up a little:
Times both sides by :
Divide both sides by :
or
If you substitute those back into the original function, you will find that they give a solution of .
If , then too. Did you follow why?
Edit: Beaten again!