Question

For the graph below, what should the domain be so that the function is at least 200?

graph of y equals minus 2 times the square of x plus 30 times x plus 200


0 ≤ x ≤ 15

−5 ≤ x ≤ 20

all real numbers

x ≥ 0

Answer 1

Answer: −5 ≤ x ≤ 20

Explanation:

Answer 2

y = 2x² + 30x + 200
y = 2(x² + 15x + 100)

x² = x*x
100 ⇒ 1 x 100 ; 2 x 50 ; 4 x 25 ; 5 x 20 ; 10 x 10

200 = 2x² + 30x + 200
0 = 2x² + 30x + 200 - 200
0 = 2x² + 30x + 0
0 = 2(x² + 15x + ?)

−5 ≤ x ≤ 20