katsuro0 Posted September 10, 2006 Share Posted September 10, 2006 how do you solve for x when: x^3 + 216 = 0 the answer should be -6, 3 + 3ÃÆâÃâ¹Ã¢â¬Â Ãâ¦Ã¡3i, 3 - 3ÃÆâÃâ¹Ã¢â¬Â Ãâ¦Ã¡3i the checkmark is a root sign i know how to get the -6 cause x^3+216=0 factors into (x+6)(x^2-6x+36)=0 but i have no idea how im supposed to get the last two parts (except from looking in the back of the book...but i have to show work, and there's like 15 problems similar to this) so help = appreciated. if i figure out how to do one of these, i can get the rest Link to comment Share on other sites More sharing options...
Guest XplsvBam Posted September 10, 2006 Share Posted September 10, 2006 well since imaginary numbers are involved all you have to do is solve it with the quadradic formula right? Link to comment Share on other sites More sharing options...
katsuro0 Posted September 10, 2006 Author Share Posted September 10, 2006 ohhhhh yea #-o Link to comment Share on other sites More sharing options...
killersushipunk Posted September 10, 2006 Share Posted September 10, 2006 no, the quadratic formula is only for quadratics. quadratics are ax^2+bx+c=0 that equation has an x^3 I would use synthetic division. I used to have a link to my school's project to provide fresh water to a Kenyan Village, but the sig police changed the link to say something, which, if followed, leads to an "ahem" adult website. Let me ask you. Which do you think is worse? Link to comment Share on other sites More sharing options...
katsuro0 Posted September 10, 2006 Author Share Posted September 10, 2006 after you factor, you have a quadratic equation. the answer came out right so ty xpls for reminding me of that annoying formula lol Link to comment Share on other sites More sharing options...
killersushipunk Posted September 10, 2006 Share Posted September 10, 2006 I would still use synthetic division in the first place. makes life so much easier \ I used to have a link to my school's project to provide fresh water to a Kenyan Village, but the sig police changed the link to say something, which, if followed, leads to an "ahem" adult website. Let me ask you. Which do you think is worse? Link to comment Share on other sites More sharing options...
katsuro0 Posted September 10, 2006 Author Share Posted September 10, 2006 i have no idea what that is though \ lol Link to comment Share on other sites More sharing options...
Guest XplsvBam Posted September 10, 2006 Share Posted September 10, 2006 after you factor, you have a quadratic equation. the answer came out right so ty xpls for reminding me of that annoying formula lol no problem, just helping you help yourself. Link to comment Share on other sites More sharing options...
KnightLite Posted September 10, 2006 Share Posted September 10, 2006 I should know this, but it's been about 4 years since I took Algebra 2. Btw... this is the part of math that you will hate most lol - Only character in Runescape History maxed out in RSC and RS2 Link to comment Share on other sites More sharing options...
katsuro0 Posted September 10, 2006 Author Share Posted September 10, 2006 im actually in college algebra and trig (we're just doing review) ...and i didn't find algebra 1 and 2 that bad :P Link to comment Share on other sites More sharing options...
Duke_Freedom Posted September 10, 2006 Share Posted September 10, 2006 And in case you hadn't seen the factors: x^3 = -216 (a+bi)^3 = -216 1) Real part: a^3-3ab^2 = -216 AND 2) Imaginary part: 3ba^2-b^3 = 0 From 2) 3) b^3 = 3ba^2 b^2 = 3a^2 From 1) and 3) 4) a^3-3ab^2 = -216 a^3-9a^3 = -216 8a^3=216 a^3=27 a=3 From 3) and 4) b^2 = 3a^2 b = 3ÃÆâÃâ¹Ã¢â¬Â Ãâ¦Ã¡3 OR -3ÃÆâÃâ¹Ã¢â¬Â Ãâ¦Ã¡3 Thus 3+3ÃÆâÃâ¹Ã¢â¬Â Ãâ¦Ã¡3i and 3-3ÃÆâÃâ¹Ã¢â¬Â Ãâ¦Ã¡3i are solutions too. ^^ The value of my bank at its height. Estimated value at the peak of the rares market: 250 billion+.Most likely the largest trade in RuneScape ever. Estimated value at the peak of the rares market: 70 billion+. Link to comment Share on other sites More sharing options...
katsuro0 Posted September 10, 2006 Author Share Posted September 10, 2006 right...lol quadratic formula ftw! Link to comment Share on other sites More sharing options...
Phil Posted September 10, 2006 Share Posted September 10, 2006 Our Policy On Homework Help Asking for help with homework is fine - feel free to do that. What we don't allow is asking for direct answers or subtley asking, "How would you do this one problem?" General explanations about homework may be given but threads asking for direct answers to problems will be locked. Link to comment Share on other sites More sharing options...
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