Homework Help Advanced Functions
Yes, yes, I shouldn't be doing this here or asking for HW help here, but honestly, I have nowhere to go.
My parents are useless in this matter, and none of my friends have maths this semester.
So here's the question:
Between 1985 through 1995, the number of home computers, in thousands, sold in Canada is estimated by
C(t) = 0.92 (t^3 + 8t^2 + 40t + 400) where t is in years, and t = 0 for 1985.
c) In what year did home computer sales reach 1.5 million?
The back of the textbook says the answer is t = 8 (so 1993) but I don't know how to get to that answer.
October 22, 2012
8 Comments • Newest first
[quote=Gyroscope]Oh boy if you're asking help for advanced functions, just wait until you get into calculus and vectors.[/quote]
My problem stems from the fact that the only method for factoring polynomial functions that my teacher knows is the factor theorem, which doesn't work here.
If I knew another method (probably what everyone else in this thread has used), I wouldn't have this problem.
@Oyster: Yes, it rounds off.
But how do you get to that exact number?
The only way my teacher has taught me (despite my insistence on being taught something else that is less akin to plugging in random numbers) was factor theorem, which is pretty useless when it comes to answers that include decimals.
Oh boy if you're asking help for advanced functions, just wait until you get into calculus and vectors.
[quote=XXsaosinXX]You plug in 8 where t is and do the equation[/quote]
If I do that, I get 1604.48.
1604.48 doesn't equal 1500 (1.5 mil / 1000).
I'm probably going about this all wrong, but what I've been doing so far has worked until now.
._.
Oh, and can you guys tell me a way of factoring polynomial functions that doesn't involve the factor theorem (the only thing my bloody teacher is willing to teach anyone)?
C(t) = 0.92 (t^3 + 8t^2 + [b]40t + 400[/b]) = 1500. Solve for t.
C(t) is in thousands.
t=7.675262457047416 yr + 1985 = 1992.68, I'm guessing your book rounds off the answer?
[Edit] Can you use the calculator to do this? If you can, just type the equation into your graphing calculator
y1 = 0.92 (t^3 + 8t^2 + [b]40t + 400[/b])
y2 = 1500
And calculate the intersection.
oops yeah, my bad thanks
[quote=flamedagger]just plug in C(t)=1500000 and solve for t by isolating t in the polynomial[/quote]
you forgot to divide 1.5 million by a thousand since the population is represented by thousands.
Sub in 1.5million (make sure to convert it to thousands aka divide by 1000) into C(t) and solve for t. it will come out as 7.67 which when rounded is 8 years so 1985+8 = 1993.
just plug in C(t)=1500000 and solve for t by isolating t in the polynomial