What is the vertex of the graph of y is equal to x squared plus 4 x ?
Answer
A
open paren negative 2 comma negative 6 close paren
B
open paren negative 2 comma negative 12 close paren
C
open paren negative 2 comma negative 4 close paren
D
open paren negative 2 comma negative 8 close paren
Explanation
For y = x² + 4x, the vertex’s x-coordinate is −b/(2a) = −4/(2 · 1) = −2. Substitute x = −2: y = (−2)² + 4(−2) = 4 − 8 = −4. The vertex is (−2, −4), choice C.
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