maths
posted by Emma
how do i find out the the equation of the line of symmetry for
f(x)=ax^2+bx+c ?
please explain it do me thanks!
The line of symmetry runs through the vertex.
so the x of the vertex is b/(2a)
and the equation of the line of symmetry is x = b/(2a)
e.g. for f(x) = 2x^2  12x + 3
after completing the square you can find the vertex to be (3,15)
or
the x of the vertex is (12)/4 = 3
then f(3) = 15.
the line of symmetry is x = 3
Quote:
The line of symmetry runs through the vertex.
so the x of the vertex is b/(2a)
and the equation of the line of symmetry is x = b/(2a)
why is the equation of symmetry for f(x)=ax^2+bx+c is x=b/2a? i still don't get this...
I suspect you need to use it a couple of times, and it will sink in .
In the meantime, Memorize: for the standard quadratic, the line of symettry is b/2a.
If you have memorized the quadratic equation, you already have it. Remember the first term in the quadratic equation?
b/2a
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