Question

The function C(x) = -2x2 + 38x + 40 models the sales, in hundreds of

Answer 1

Question:

Rewrite the function to reveal when sales of compact discs and $0.

Answer:

The cost in 2010 is $0

Step-by-step explanation:

Given

$C(x) = -2x^2 + 38x + 40$

Required

Find x when $C(x) = 0$

This gives:

$C(x) = -2x^2 + 38x + 40$

$-2x^2 + 38x + 40=0$

Expand

$-2x^2 + 40x -2x+ 40=0$

Factorize:

$-2x(x - 20) -2(x- 20)=0$

$(-2x - 2)(x- 20)=0$

Solve for x

$-2x-2=0\ or\ x - 20 = 0$

$x = -1\ or\ x = 20$

x represents time.  So, it cannot be negative.

$x = 20$

20 years after 1990 is: 2010. Hence, the cost in 2010 is $0