A quadratic function is given.

Algebra
Tutor: None Selected Time limit: 1 Day

f(x) = −4x2 − 16x + 1

(b) Find its vertex and its x- and y-intercept(s). (If an answer does not exist, enter DNE.) 

vertex    (xy) =
  
x-intercepts    (xy) =
  
 (smaller x-value)
(xy) =
  
 (larger x-value)
y-intercept    (xy) =
  


Mar 4th, 2015

Using the quadratic formula the roots are given by:

x = [ -b +/- sqrt( b^2 - 4ac) ] 2a where a = -4, b = -16 and c = 1

x = -2 +/- sqrt(17)/2

So x-intercepts are (-2-sqrt(17)/2 , 0) and (-2+sqrt(17)/2 , 0).

y-intercept is simply (0, f(0)) = (0, 1)

The vertex form is given by y = a(x – h)^2 + k, where (h, k) is the vertex. We can calculate it using: 

h = −b/2a = 16/8 = 2

k = c - b^2/4a = 1 - 16^2 / -16 = 17

So the vertex is (2,17).

Mar 4th, 2015

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