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thread starter Toledoll Aug 28 2010 + PM | QUOTE | PERMALINK | REPORT

I've searched and searched the math links and have yet to come up with anything that helps me. I need to find the domain of the function: cubed root of x^2+3x.

My Characters: Toledoll - 73 Windia I/L Mage

Beca + PM | QUOTE | PERMALINK | REPORT

0 to infinite? >.< Oh wait, cubed root. Haha.

My Characters: PandaYoshi - 43 Scania Fighter

Toledoll 08/28/10 + PM | QUOTE | PERMALINK | REPORT

It's killing me. D:

My Characters: Toledoll - 73 Windia I/L Mage

ShiverStar + PM | QUOTE | PERMALINK | REPORT

I'm fairly certain x = all real numbers. If it were a square root (or any even root), you would have to exclude any value where x^2+3x is negative.

My Characters: LorskSin - 30 Khaini Assassin

Toledoll 08/28/10 + PM | QUOTE | PERMALINK | REPORT

[quote] ShiverStar : I'm fairly certain x = all real numbers. If it were a square root, you would have to exclude any value where x^2+3x is negative. [/quote] Could you explain how to work it out? I have to show work and I'd like to understand it later.

My Characters: Toledoll - 73 Windia I/L Mage

tangentline 08/28/10 + PM | QUOTE | PERMALINK | REPORT

Basically every number you can take the cube root of... -infinite to infinite.

My Characters: cwknoob - 75 Scania Rogue

bombinator 08/28/10 + PM | QUOTE | PERMALINK | REPORT

http://www.wolframalpha.com/input/?i=%28x^2%2B3x%29^%281%2F3%29 Maybe this will help.

My Characters: Lon3Sin - 124 Broa Hermit

wr4thbr1nger 08/28/10 + PM | QUOTE | PERMALINK | REPORT

if you have trouble seeing it like that, answer: what is the domain of (the cube root of B?) and B=the thing inside the root

My Characters: d4rk3rb4nd1t - 94 Bera Chief Bandit

Toledoll 08/28/10 + PM | QUOTE | PERMALINK | REPORT

[quote] bombinator : http://www.wolframalpha.com/input/?i=%28x^2%2B3x%29^%281%2F3%29 Maybe this will help. [/quote] It helps with knowing the answers and seeing the graph, but I'm supposed to be able to show work on my paper somehow.

My Characters: Toledoll - 73 Windia I/L Mage

Rafflesia + PM | QUOTE | PERMALINK | REPORT

Problem: cubed root of x^2+3x x^2+3x=y cubed root of y domain of cubed root of y is all real numbers domain of x^2+3x is all real numbers If the problem was square root of x^2+3x then your work would be x^2+3x=y domain of square root of y is x>0 x^2+3x>0 x(x+3)>0 x>0 x>-3 plug in -1 (between 0 and -3) (-1)^2-3=-2 which isn't >0 so the domain doesn't include numbers from -3 to 0 so the answer would be x>0

My Characters: Heda - 87 Bera Ranger

ShiverStar 08/28/10 + PM | QUOTE | PERMALINK | REPORT

[quote] Toledoll : Could you explain how to work it out? I have to show work and I'd like to understand it later. [/quote] The domain of a function is simply the range of x values that will yield a real number when plugged in to the equation. Because all numbers have a cube root, any value of x^2+3x will work. I'm not sure how to mathematically prove this, if that's what your teacher is looking for.

My Characters: LorskSin - 30 Khaini Assassin

Toledoll 08/28/10 + PM | QUOTE | PERMALINK | REPORT

My bad, it's actually supposed to be the 4th root, not the cubed root. I still need help, though. >.<

My Characters: Toledoll - 73 Windia I/L Mage

tangentline 08/28/10 + PM | QUOTE | PERMALINK | REPORT

You don't really show work for domain and range... Show a graph?

My Characters: cwknoob - 75 Scania Rogue

Rafflesia 08/28/10 + PM | QUOTE | PERMALINK | REPORT

[quote] Toledoll : My bad, it's actually supposed to be the 4th root, not the cubed root. I still need help, though. >.< [/quote] Ugh Way to go. PM me and I'll help you.

My Characters: Heda - 87 Bera Ranger

bombinator 08/28/10 + PM | QUOTE | PERMALINK | REPORT

[quote] Toledoll : It helps with knowing the answers and seeing the graph, but I'm supposed to be able to show work on my paper somehow. [/quote] [x^2 + 3x]^(1/4) [x(x + 3)]^(1/4) Set equation to zero, find what the roots are and test each of the intervals. [x(x + 3)]^(1/4) => 0 x = 0, x = -3 ~~~ -3 ~~~ 0 ~~~ Use test values from each of the intervals [as seen in curly hyphens], test them to ensure they work, and that information will be included in your domain. Test values: -4, -1, 1 [ (-4) ( (-4) + 3)]^[1/4] => 0 (-4[-1])^[1/4] => 0 4^[1/4] => 0 Above: So anything less or equal to -3 is part of the domain. [ (-1) ( (-1) + 3)]^[1/4] => 0 (-1[2])^[1/4] => 0 -2^[1/4] => 0 Above: Anything between -3 and 0 does not exist. [ (1) ( (1) + 3)]^[1/4] => 0 (1[4])^[1/4] => 0 4^[1/4] >= 0 Above: Anything greater or equal to 0 is part of the domain. Your solution: [x/x <= -3, x => 0, where x is any real number] or x <= -3 and x >= 0. Btw, <= is the symbol 'less than or equal to', >= is the symbol 'greater than or equal to'. Hope this helped.

My Characters: Lon3Sin - 124 Broa Hermit