A simple maths question?

Question

My graph is'nt really looking right so just wondering if you guys get the same points i do:
y=2x^2-4x-1
And of course we are asked to fill in the x/y grid and plot the graph - so we have to put in -1 to the equation and +1 as x's value - just wondering what two numbers you get? I got -3 and 3?

Answer 1

You should get a parabola, opening upwards, that crosses the y-axis at (0, -1), and with a vertex at (1, -3).

Plotting the point with x value of 1 should give you (1, -3),
and plotting the pt w/ x value of -1 should give you (-1, 5), not (-1, 3)
(because 2(-1)² -4(-1) -1 = 2 + 4 - 1 = 5).

Hope that helps! :)

Answer 2

When x = -1, y = 5

y = 2x^2-4x-1

y = 2(-1)^2-4(-1)-1 when you square -1 it becomes positive
y = 2(1)-4(-1)-1
y = 2+4-1
y = 2+3
y = 5

When x = 1, y = -3

y = 2x^2-4x-1

y = 2(1)^2-4(1)-1
y = 2(1)-4(1)-1
y = 2-4-1
y = 2-5
y = -3

plot these values you should get a parabola that opens upward, with a minimum value at (1,-3)

( x y)
(-1 5)
(-.2247, 0)
(1,-3) minimum
(2,-1)
(2.2227,0)
(3,5)

Answer 3

When x = 1:
y = 2(1)^2 - 4(1) - 1
y = 2 - 4 -1
y = -3

When x = -1:
y = 2(-1)^2 - 4(-1) - 1
y = 2 + 4 - 1
y = 5

So your points should be (1, -3) and (-1, 5). It looks like (1, -3) is the vertex of the parabola, when you graph it. See the link below...

Answer 4

When x = -1
y = 2(-1)^2 -4(-1) - 1 = 2(1) + 4 - 1 = 5

When x = 1
y = 2(1)^2 - 4 (1) - 1 = 2 - 4 - 1 = -3

Answer 5

-1 = x means
y = 2(-1)^2 - 4(-1) -1
y = 2*1+4-1
y = 2+4-1
y = 6-1
y = 5
(-1,5) is one point

+1 = x means
y = 2(1)^2 - 4(1) -1
y = 2*1 - 4 -1
y = 2-4-1
y = -2-1
y = -3
(1,-3) is the second point.

Hope this helps. Good luck with graphing. :)

Answer 6

Should be a parabola -
Coordinates -
(-2, 15) (-1, 5), (0, -1), (1, -3), (2, -1)
For y=2x^2-4x-1

Answer 7

when x=-1 y=5
when x=1 y=-4

Answer 8

I get (-1,5) and (1,-7)