Question

without drawing the graph of the equation, determine how many points the parabola has in common with the x-axis and whether its vertex lies above, on, or below the x-axis.
y=2x^2+x-3

A. 2 points in common; vertex below x-axis
B. no points in common; vertex below x-axis
C. 1 point in common; vertex on x-axis
D. 2 points in common; vertex above x-axis

Answer 1

Do you know how to tell whether the graph opens up or down?

Answer 2

if the coefficient of x² is positive the parabola opens up. If it's negative the parabola opens down

Answer 3

and to find the x-coordinate of the vertex use x = -b/(2a)

Answer 4

so, the coefficient of x^2 is 2, right?

Answer 5

right

Answer 6

so which way does the parabola open?

Answer 7

up

Answer 8

ok. so now let's find the vertex. For a quadratic equation ax²+bx+c, the x-coordinate of the vertex is \[x=\frac{ -b }{ 2a }\]

Answer 9

i got -1/4=-0.25

Answer 10

right. Now plug -1/4 in for x in your original formula to find the y-coordinate.

Answer 11

i got -4.25? which answer is that?

Answer 12

I got -3.125

Answer 13

show me what you did, please