Points on a graph?

Question

If I have the points

(-3,-18)
(-2,-10)
(-1,-4)
(0,0)
(1,4)

with the equation y = x^2 +3x

What is my axis of symmetry????????

Answer 1

y=x^2+3x means the graph is a parabola

set y=0 x^2+3x=0 yields x values of 0, -3

These are the points where the graph cuts the x axis

since the parabola is symmetric, the axis of symmetry is the mid-point of 0 and -3. ie at -1.5.

The axis of symmetry is x=-1.5

Answer 2

Wow, its been a while for me, but axis of symmetry means the point when that line crosses the y axis, meaning when your y equals 0, then that is your axis for the equation. Your axis in your example would be at the point 0,0, since y equals 0 then.

When in doubt finding your axis, solve your equation for y....that is the point where the line crosses the y (horizontal line) axis. Make y equal 0, so that in your example, xsquared plus 3x equals 0.....the only way it works, by algebra is if x equals 0 zero is both your y axis of when that line crosses, and the x coordinate.

Take this example, also......y=2x +2 the y axis would be -1, since when y =0, x=-1 your axis of symmetry would be the point -1,0

Always set y=0 to find your axis, it is easy and that is how my instructor taught me to do it, not sure if its the best or easiest, but it always works.

I hope this helps and good luck...

Answer 3

the axis of symmetry of any Parabolic function in form y = ax^2 + bx +c is : y = -b / 2a thus
in this case, it is y = -3/2