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| Acmlm's Board - I2 Archive - Brain Teasers - Strange Math Riddles |
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ziratha Ninji Level: 24 Posts: 20/231 EXP: 77808 For next: 317 Since: 06-29-04 Since last post: 4 days Last activity: 17 days |
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| abx+2abx=40a 8b+6=2x 4b+3=x ab(4b+3)+2ab(4b+3)=40a 12ab^2+9ab=40a 12b^2+9b=40 (-9+-(81-4*12*-40)^.5)/24 (-9+-(2001)^0.5)/24 ignore this, apparently im wrong....(heian, i think u did: ,(81+4*12*-40)=-1839,ill look really stupid if im wrong now...) (-9+-44.73)/24 (-3+-14.91)/8 ill divide and round to 2 decimal places b=11.91/8=1.48875=1.49,x=5.96+3=8.96 Or b=-17.91/8,=-2.23875=-2.24,x= -8.96+3= -5.96 now to check. bx+2bx=40 1.49*8.96*3=38.8443, close to 40, seems right with the rounding. Or -2.24*-5.96*3=40.0512, even closer. (edited by ziratha on 08-04-04 09:14 PM) (edited by ziratha on 08-04-04 11:47 PM) |
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JJ64 Boo Level: 45 Posts: 914/919 EXP: 640956 For next: 19208 Since: 05-22-04 From: Green Bay, WI Since last post: 441 days Last activity: 269 days |
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| Heian-794 has the point, my browser is having problems, I can't post anything longer than a line, so you'll get the next question later... | |||
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ziratha Ninji Level: 24 Posts: 21/231 EXP: 77808 For next: 317 Since: 06-29-04 Since last post: 4 days Last activity: 17 days |
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| Damn i look like an idiot.... o well, im used to it. I'm gonna run our answers through my calculatot, figure out where i miscalculated anyway this part of his math seems wrong, or did i totally forget the quadratic equation??? i looked at heians work and this is what i came up with, would somebody please tell me what im doing wrong, i really cant for the life of me. from heians... 12b2 + 9b - 40 = 0 Using the quadratic formula, we arrive at: b = (-9 +/- sqrt(-1839)) / 24 b = (-3 +/- 613i)/8 12b2 + 9b - 40 = 0 the quadratic equation should be (-b+-/squrt(b^2-4*a*c))/2a right? or am i totally wrong???????? (-9+-/squrt(9^2-4*12*-40))/24 0=(-9 +/- sqrt(-1839)) / 24 how can -4*9*-40 = a negative number??? -4*-40=160 and 12*160=1920 1920+81=2001... ,..... ...... I must be doing something, wrong, can anybody point it out? cause if i am i want to know so that i can get questions right. This is really bothering me.... anyway ill check his answers on my calculator cause i did mine and they seemed right, ill check them after i check his..... his answers are: b = (-3 +/- 613i)/8 and x = [(-3 +/- 613i)/2] + 3 = (3 +/- 613i)/2 abx+2abx=40a 8b+6=2x 3bx=40 3((-3+613i)/2)*((3+613i)/2)= -3(-9/2-1839i/2+1839i/2+375769i^2)=-3(-9/2-375769/2)=-563667?????what am i doing wrong..???????/ i must be a total idiot....  3((-3-613i)/2)*((3-613i)/2)= -3(-9/2=1839i/2-1839i/2+375769i^2)=-3(-9/2-375769/2)=-563667????? seems to come to the same answer. im realllyyy confused..... (edited by ziratha on 08-04-04 11:50 PM) (edited by ziratha on 08-05-04 12:00 AM) (edited by ziratha on 08-05-04 12:35 AM) |
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Heian-794 Red Super Koopa Level: 44 Posts: 366/896 EXP: 611014 For next: 271 Since: 06-01-04 From: Kyoto, Japan Since last post: 21 days Last activity: 10 days |
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| JJ, it looks like I missed a minus sign in the quadratic formula and that Ziratha's answer of b = (-9 +/- sqrt(2001)) / 24 is correct (i. e. 2001 under the root sign, not -1839). This makes X (after some reducing) (9 +/- sqrt(2001)) / 6. Did you make the same mistake? The square root of 2001 is 44.7325, so we've got 1.4889 or -2.2389 for B and 8.9554 or -5.955 for X Pairing the first B with the first X, and the second B with the second X, gives us 40 to three decimal places. So the only problem with Ziratha's answer was that he rounded too quickly, whereas I missed a whole minus sign. I think he should have the point on this one. |
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ziratha Ninji Level: 24 Posts: 22/231 EXP: 77808 For next: 317 Since: 06-29-04 Since last post: 4 days Last activity: 17 days |
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You mean... im not an idiot? ... ahem yay yay ayyaay, I was certain i was gonna get a bag over the head point in this quiz game too... anyway thanks heian.  ... I'm really tired.. Im not sure IF ill be back today ... |
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JJ64 Boo Level: 45 Posts: 917/919 EXP: 640956 For next: 19208 Since: 05-22-04 From: Green Bay, WI Since last post: 441 days Last activity: 269 days |
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| I first ended up with your answer also, Heian, now I realize my mistake... Scores 1st. Grey-22 points 1st. Heian-794-22 points 3rd. NSNick-10 points 4th. Kirby all the way-8 points 5th. wolfman2000-5 points 6th. ziratha-4 points 7th. Emptyeye-1 point 7th. RavenX-1 point 7th. Slash Dafter-1 point 7th. Xkeeper-1 point 11th. neotransotaku-0 points 11th. Gb boy-0 points 11th. Teddylot-0 points Question 75 (1 point)- Solve for x: 7x^3+2x^2-9x+7=253 |
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Heian-794 Red Super Koopa Level: 44 Posts: 373/896 EXP: 611014 For next: 271 Since: 06-01-04 From: Kyoto, Japan Since last post: 21 days Last activity: 10 days |
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| 7x� + 2x� - 9x - 246 = 0 I didn't know the formula for solving cubic equations so I had to look it up. Here goes: We need to first define three intermediate-step numbers f, g, and h: f = [(3c/a) - (b�/a�  ] /3 = .25853g = [(2b�/a� - (9bc/a� + (27d/a)] / 27 = 41.1445h = (g�/4) + (f�/27) = 423.2288 If h is positive (which it is), we then define three more intermediate numbers: R = -(g/2) + sqrt(h) = .000275 (note that the square root of H is really close to -1/2 of G, meaning that we have to worry about rounding error) S = (R)^(1/3) = .06504 T = -(g/2) - (h) = -443.80105 U = T^(1/3) = -7.6277 Now: X1 = (S + U) - (b/3a) X2 = -(S + U)/2 - (b/3a) + i*(S-U)*sqrt(3)/2 X3 = -(S + U)/2 - (b/3a) - i*(S-U)*sqrt(3)/2 (this is -X2) Which gives us: 3.3101 and -1.7979 +/- 2.7174i Edit: I won't be able to post for three days or so starting tomorrow. Don't score too many points while I'm gone! (edited by Heian-794 on 08-08-04 02:11 PM) |
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Dylan Devil Trumpets and Angel Trombones ~ Level: 54  Posts: 643/1407 EXP: 1181697 For next: 52173 Since: 06-19-04 From: Ottawa, Canada. Since last post: 1 day Last activity: 6 hours |
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I guess JJ is on vacation. He needs to give us a question soon before this gets buried.  |
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Heian-794 Red Super Koopa Level: 44 Posts: 379/896 EXP: 611014 For next: 271 Since: 06-01-04 From: Kyoto, Japan Since last post: 21 days Last activity: 10 days |
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| Maybe he's building up the suspense of the 22-22 tie for the lead! How many questions are in this one? A hundred? When it's over, I might want to start my own math quiz. |
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Grey the Stampede Don't mess with powers you don't understand. And yes. That means donuts. Level: 82  Posts: 635/3770 EXP: 5192909 For next: 16318 Since: 06-17-04 From: Kingston, RI, USA, Earth Since last post: 2 hours Last activity: 1 hour |
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| It's 100, but I'm dropping out to play Mindtrap and 20 Questions... I'd still love to see what JJ can throw at us though, some of these questions are pretty challenging. |
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Dylan Devil Trumpets and Angel Trombones ~ Level: 54 Posts: 683/1407 EXP: 1181697 For next: 52173 Since: 06-19-04 From: Ottawa, Canada. Since last post: 1 day Last activity: 6 hours |
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| I bet the word problems are from a site or book, I doubt he would take the time to create a tough word problem that turns out logical. Now if we could only find that site... ha. HA. Actually, I'd prefer to solve them myself, thats the whole point of a brain teaser.  |
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| Acmlm's Board - I2 Archive - Brain Teasers - Strange Math Riddles |
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