Continuous random variable={-b-(b^2-4ac)^.5}/(2a)=x?

[inv]

[Solved]Continuous random variable={-b-(b^2-4ac)^.5}/(2a)=x?

Homework Statement

A factory is supplied with grain at the beginning of ea week.The weekly demand,X thousand tonnes for grain from this factory is a continuous random variable having the probability density function given by
f(x)=2(1-x),0<x<1
0 ,otherwise
Find the quantity of grain in tonnes the factory should've in stock in the beginning of a week in order to be 98% certain that the demand in that week will be met.

*I've found 2 answers but the answer sheet only chose 1 of 'em,found by using the (-b-(b^2-4ac)^.5)/(2a)

Homework Equations

(-b+(b^2-4ac)^.5)/(2a)

The Attempt at a Solution

I've integrated f(x) with the lower x value and higher x value 0 and 1 respectively and got:
[2x-x^2]=0.98
0=x^2-2x+0.98
(-b+(b^2-4ac)^.5)/(2a)
x=1.14 and 0.859
*I don't know why the answer sheet chose only the 0.859,why?

 

[cristo]

*I don't know why the answer sheet chose only the 0.859,why?

What's the domain of f in the orginal question?

 

[inv]

Domain of f is x,domain is x and range is y.That's what u want?

 

[cristo]

Domain of f is x,domain is x and range is y.That's what u want?

No, sorry, I'll rephrase my question. The function f is only defined for certain values of x. What are these? Are both of your answers in the interval of allowed x values?

 

[inv]

Nnly 1 of 'em're,which makes this case solved.Tq so much for making me realize.

 

[HallsofIvy]

Domain of f is x,domain is x and range is y.That's what u want?

No, the domain of a function is the set of possible values for x- and those are given in the problem.

 

[inv]

Thanks for the reply a bunch Ivy ,bye.