znimon
How do I find the domain of this function?
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znimon
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\[g(x) \sqrt{x^2 - 3x - 40}\]
znimon
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I have \[\sqrt{(x-8)(x+5)} \]
znimon
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\[(x-8)(x+5) \ge 0\]
znimon
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The original problem is at the top.
Yahoo!
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Draw a number line and see for it
znimon
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I don't know what x can't be though
znimon
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I know the answer but I don't know how to get the answer.
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(-infinity , 5] U [8 , infinity)
znimon
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yeah but how do I find that?
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just do trial and error method...)
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(x−8)(x+5)≥0
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luk for the vlue of x which satisfies this...
znimon
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There must be a logical way to find the answer, right?
ganeshie8
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(x-8)(x+5) >= 0
its a parabola, right ?
znimon
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I could input it into my graphing calculator but other wise I don't know how to tell if its a parabola or not.
ganeshie8
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y = ax^2 + bx + c is a parabola
ganeshie8
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any quadratic function gives a parabola graph
znimon
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ok
ganeshie8
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can you find the x intercepts ?
ganeshie8
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once you find x-intercepts, you would know where the parabola dips into x axis (goes negative)
ganeshie8
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|dw:1346519548989:dw|
znimon
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Oh ya that would be the point at which the g(x) function is 0, so its x - 8 = 0, x = 8, x+ 5 = 0, x=-5, and since its a parabola the graph only passes through zero twice. Nice dude, so the domain is (-infinity, -5] U [8, +infinity]
ganeshie8
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yeah nice you got it :)
znimon
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@ganeshie8
znimon
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Awesome, thanks again. Is there a way I could recognize any graph's shape or at least some and would you recommend memorizing those?
ganeshie8
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if the degree is 2, then its a parabola
ganeshie8
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finding domains for other polynomials is bit tricky... as they may dip into x-axis multiple times
znimon
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okay
ganeshie8
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do you knw sketching polynomilas (end behiavior thingy )
znimon
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never heard of it
ganeshie8
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end behavior helps you sketch ANY polynomial freehand
znimon
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Thanks dude, I'll look it up
ganeshie8
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process is basically :
1) find x intercepts
2) using end-behavior sketch the graph by hand
ganeshie8
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its easy concept and worth learning... im sure you wil get hang of it in few minutes....... good luck :)
znimon
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why is it that a polynomial with a degree of two is a parabola?
znimon
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Thanks again.
ganeshie8
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uhh il have to think...... idk exactly... i think it has something to do with local maximum/minimum + increasing/decreasing thingy. we need to turn to calculus for proper understanding. im also learning... . so im no good for answering this :(
ganeshie8
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@mukushla @eliassaab @experimentX
znimon
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Oh, I have enough to learn for now so it doesn't matter to me. I bet I wouldn't understand the explanation if it involves terms I've never had before haha.