Mathematics

Emery Crosby

14 October, 22:44

Jan'ai was asked to determine the minimum for a function with zeros located at - 1 and 5, which also has a y-intercept of (0,25). Her work is shown.

Begin to write a function in factored form. f (x) = a (x+1) (x-5)

Substitute to determine a. - 25 = a (0+1) (0-5)

Simplify and solve to find a. a=5

Rewrite the function. f (x) = 5 (x+1) (x-5)

Rewrite in standard form. f (x) = 5x^2-20x-25

Find the x-coordinate of the vertex. x = - 20/2 (5) = - 20/10; x = - 2

Find the y-coordinate of the vertex. y = 5x^2-20x-25

y = 5 (-2) ^2-20 (-2) - 25

y = 35 so (-2,35)

Which best describes the first error in Jan'ai's work?

A) She incorrectly determined the factors for the beginning function.

B) She incorrectly determined the a value.

C) She incorrectly transformed the equation to standard form.

D) She incorrectly determined the x-coordinate of the vertex.