SOLUTION: Hi, my word problem is A population of crocodile is a game reserve after t years can be modelled by the equation 42t^2+36t+1008. after how may years will the population be equal

Question 800723: Hi, my word problem is
A population of crocodile is a game reserve after t years can be modelled by the equation 42t^2+36t+1008. after how may years will the population be equal to 1620? use the formula t= -5+-sqrt(b^2-4ac)/2.
I have done the problem to where I get 36+-sqrt(-168048)/84 and know I don't know how to complete this problem any further. my e-mail address is; dejagero@gmail.com
I will appreciate your help, I hae sleepless knight over this problem
Found 2 solutions by KMST, Cromlix:
Answer by KMST(5328) (Show Source): You can put this solution on YOUR website!
The formula given is not for applying blindly to a polynomial.
It is used to apply to a quadratic equation of the form ,
meaning an equation that says that a quadratic polynomial .

To get from your problem to such an equation, whose solutions would be given by

you have to start by stating (in algebra language) that the population equals 1620,
and then do some manipulation to get to the form with that zero on one side of the equal sign.

--> -->
With the term without being opposite in sign to the coefficient of you are assured to get a positive number under the square root.
Also, at any point in the line above, you could realize that everything is divisible by 6, and dividing by 6 makes the numbers smaller.
For example,
--> --> -->
That simplification is not absolutely needed, but helps if you are prone to make mistakes when writing long numbers.

Then, you apply the formula, but the minus sign in front of the square root will give you a negative result, which would not make sense for the problem, so the useful result will be calculated as
= approximately =approximately
or as
= approximately =approximately
Answer by Cromlix(4381) (Show Source): You can put this solution on YOUR website!
42t^2+36t+1008 Equation
42t^2+36t+1008 = 1620
42t^2+36t+1008 - 1620 = 0
42t^2+36t-612 = 0
Divide throughout by 6
7t^2 + 6t - 102 = 0

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