without drawing the graph of the equation, determine how many points the parabo.

Algebra
Tutor: None Selected Time limit: 1 Day

determine how many points the parabola has in common with the x-axis and whether its vetex lies above on or below the x axis.

y=-2x^2+x-3

Mar 10th, 2015

We can see from the fact that x^2 term is negative that the parabola goes to -infinity as |x| gets large (it forms an inverted-u shape).

We can also rearrange this standard form quadratic (y = ax^2 + bx + c) into vertex form (y = a(x - h)^2 + k):

y=-2x^2+x-3

= -2(x^2 -x/2 +3/2)

= -2(x - 1/4)^2 + 3/2-1/16

Since (h,k) is the vertex we just need to check whether k is positive or negative. It is positive, so the vertex lies above the x-axis. And since the parabola curves down, it will cross the x-axis at two points.

Mar 10th, 2015

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