The function C(x)=-2x^2 +38x+40 models the sales, in hundreds of millions of dollars, of compact discs for years since 1990. Part A: Rewrite the function to reveal when sales of compact discs and $0.

Part B: What are the zeros of the function?

Part C: Use the context to interpret the zeros.

hello from mrbilldoesmath!

answer:

25x^2 + 90x + 84

discussion:

mn(x) = m(n(x)) = m( 5x + 9) =

(5x + 9)^2 + 3 =>

25x^2 + 90x + 9^2 + 3 =

25x^2 + 90x + 84                 (as 9^2 = 9*9 = 81)

which is the second choice

regards,  

mrb

p.s.   i'll be on vacation from friday, dec 22 to jan 2, 2019. have a great new year!