Finding the domain

[sondang]

I was just wondering the different ways I could find the domain for the question below

Eg. the equation is: A(x)=-x^2 + 92x - 720. There can't be any negative values because I'm finding the maximum possible area of a shape. (A = area)

The question is: "State a suitable domain of the function A(x)".

I was thinking of factorising it finding the domain from there but I can't factorise that equation with my brain so are there any other ways of doing it??

Help greatly appreciated! Thanks

[507]

Probably better to complete the square or use the quadratic formula to find the x-intercepts in this problem.










So your domain is

[sondang]

Sorry I should've just showed the whole question instead of trying to ask questions that wouldn't help me. I appreciate your help though!

Here's the question.

"The dimensions of en enclosure are shown. The perimeter of the enclosure is 160m."

<---- here's the diagram

a) find the rule for the area, A m^2, of the enclosure in terms of x.

I worked it out, checked the answer at the back of the book and it's: A(X)=-x^2 + 92x - 720

Now the question I was trying to get help was this

b) State a suitable domain of the function A(X).

[BubbleWrapMan]

You can see from the shape that y has to be at least 20 metres, and x has to be at least 12 metres

You would have found that y = 80 - x. If this is greater than 20, you get 80 - x > 20, so x < 60.

So the allowable values of x are 12 < x < 60

[sondang]

You can see from the shape that y has to be at least 20 metres, and x has to be at least 12 metres

You would have found that y = 80 - x. If this is greater than 20, you get 80 - x > 20, so x < 60.

So the allowable values of x are 12 < x < 60

Perfect! That was the exact answer at the back of the book. Thanks a lot!!