Question

The volume of the shipping box needs to be 1,144 cubic inches. The equation that models the volume of the shipping box is 8(n + 2)(n + 4) = 1,144.

Answer the following questions about the equation modeling the volume of the shipping box.

Question 1

Solve the equation that models the volume of the shipping box, 8(n + 2)(n + 4) = 1,144. If you get two solutions, are they both reasonable?

Answer 1

n = 9

Explanation:

8(n + 2)(n + 4) = 1,144

(n + 2)(n + 4) = 143

n² + 2n + 4n + 8 = 143

n² + 6n - 135 = 0

n² + 15n - 9n - 135 = 0

n(n + 15) - 9(n + 15) = 0

(n - 9)(n + 15) = 0

n = 9, -15

since n is a length, it can not be negative

Therefore the only solution is n = 9

Answer 2

see below

Explanation:

8(n + 2)(n + 4) = 1,144

FOIL

8(n^2 +2n+4n+8) = 1144

Divide each side by 8

8/8(n^2 +2n+4n+8) = 1144/8

(n^2 +2n+4n+8) = 143

Combine like terms

n^2 +6n+8 = 143

Subtract 143 from each side

n^2 +6n+8 -143= 0

Combine like terms

n^2 +6n -135 =0

Factor

What two terms multiply to -135 and add to 6

-9*15 =-135

-9+15 = 6

(n-9) (n+15) =0

Using the zero product property

n-9 =0 n+15=0

n = 9 n=-15

The length cannot be negative so n = -15 cannot be a solution

n =9