How do I find the domain and range of these questions? (1 Viewer)

DrDawn

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Can anyone help me out with finding the domain and range of these questions (algebraically, not graphically), any advice or tips is appreciated, thanks so much! :)


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dumNerd

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Can anyone help me out with finding the domain and range of these questions (algebraically, not graphically), any advice or tips is appreciated, thanks so much! :)


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For fractions remeber the bottom cannot be 0 or it would be no solution. And for roots the inside has to he bigger than or = 0. These are hints now u can figure it out
 

YonOra

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Cool so, for the domain I like to look at the denominator first. We know nothing can be divided by 0. So for example a), you can see that x =/ -2, and x > -2 also wont work as that'll be a sqr root of a neg No. So now we can say x can be any number greater than or equal to -2. So your domain is x >-2 or x ∈ (-2, ∞).
 

YonOra

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Now the sexy part - algebra.

Take e) for example:
We know that whatever is inside the sqr root must be greater than or equal to 0.
So,
x^2 - 4 ≥ 0
(x-2)(x+2) ≥ 0
Do this whatever way you've been taught to, if you want help, lmk.

Now you have your domain, -2 ≥ x, x ≥ 2.
 

YonOra

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Sorry, I assumed range would be given. For the example above (e)), you can sub in both x values into the equation, and you'll get 0, but you also know that whatever is in the sqr root MUST be positive (because of x^2... i.e. (-1)^2 = 1), therefore we can say R; y ≥ 0
 

DrDawn

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For fractions remeber the bottom cannot be 0 or it would be no solution. And for roots the inside has to he bigger than or = 0. These are hints now u can figure it out
I understand how to figure out the domain but finding the range is difficult, how do you find it?
 

Trebla

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If you’re not too good at inspecting the equation to find the minimum/maximum values of y, then you can use calculus to investigate the nature of turning points.
 

DrDawn

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Btw does anyone know where I can find more questions like these?
 

YonOra

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If you’re not too good at inspecting the equation to find the minimum/maximum values of y, then you can use calculus to investigate the nature of turning points.
F.D.T for life
 

DrDawn

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Also how do you solve for the range when the numerator is x? (for question a)
 

DrDawn

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Yes, by finding the maximum and minimum turning points, though you’re effectively trying to find the properties of the graph in doing so.
I'm so sorry but could you please explain how to find the max and min turning points?
 

DrDawn

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Ok so basically you have to draw a rough sketch of the graph to find the range (or alternatively you can do calculus), and for domain you can find it by solving the equation in the denominator (thus finding the asymptotes and domain)
 

Trebla

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Ok so basically you have to draw a rough sketch of the graph to find the range (or alternatively you can do calculus), and for domain you can find it by solving the equation in the denominator (thus finding the asymptotes and domain)
It’s better to think of these as “tools” you could potentially use rather than as prescribed methods. Techniques like “solving the equation of the denominator” don’t work if the function doesn’t have a denominator to solve in the first place!

At the end of the day your goal is just to find the all the allowable x values and allowable y values for a function. There are many ways to go about doing that and some techniques only work for specific types of functions.
 

DrDawn

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And yes, I do agree with Trebla above, that it’s better to think of these as “tools” you could potentially use rather than as prescribed methods.
However, I do understand that some people prefer to learn with a clear method, and if that's what you want to use, that should be fine too!
I don't want to use those tools too often because it only works for certain equations so what would be a "clear" method to solve these?
 

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