Question

Find the range of the quadratic function.

f(x) = -x2 + 4x - 8
A) [2, ∞)
B) [-4, ∞)
C) (-∞, -4]
D) (-∞, 2]

Answer 1

find the vertex using -b/(2a)... this is the x-coordinate of the vertex.
then you must determine if the parabola opens upwards or downwards...

can you give the vertex?

Answer 2

yeah i think

Answer 3

(2,-4)

Answer 4

yes... that's the vertex...
now do you know if the parabola opens upwards or downwards?

Answer 5

It opens downwards because the coefficient of x^2 is negative which means the parabola goes infinitely downward hence tha range is from negative infinity to the highest vertical point which is the -4 in (2,-4) so the answer is C.

Answer 6

thanks

Answer 7

No problem.

Answer 8

f(x) = -x^2 + 4x - 8
find the vertex

(h,k)
h = -b/2a = -4/(-2*1)=2
k = -x^2 + 4x - 8 =-2^2 + 4*2 - 8 = -4 + 8 -8=0

so vertex (2,-4)

now lets draw it
-x^2 will make it open downward