Solve for fun:





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Discus: High School Life and Pre-college Issues: May, 2003 and Earlier Archive: Solve for fun:
By Ramirez7 (Ramirez7) on Tuesday, April 01, 2003 - 01:05 am: Edit

x2-4x+18=0

By Mrpancake2000 (Mrpancake2000) on Tuesday, April 01, 2003 - 08:48 am: Edit

2 plus or minus 2i times the square root of 14, no?

By Dumbuket (Dumbuket) on Friday, April 04, 2003 - 04:14 pm: Edit

umm... quadratic equation, u dumb fuhkahs!!!

By Bhs4life (Bhs4life) on Friday, April 04, 2003 - 04:15 pm: Edit

x=9

By Zerg_Vvins (Zerg_Vvins) on Saturday, April 12, 2003 - 04:46 pm: Edit

use this:

the answer is 4 plus or minus square root of -56 over 2

By Worth2try (Worth2try) on Tuesday, April 22, 2003 - 12:11 pm: Edit

I got 9 too

By Brd (Brd) on Tuesday, April 22, 2003 - 12:34 pm: Edit

If you got x=9, you should consider a review of algebra. In any event, it's always good to check your answers. It only takes a glance to see that:

81 - 36 + 18

cannot possibly equal zero.

Zerg has the correct answer. (MrPancake probably had the correct answer but made a mistake simplifying; he forgot to cancel a two in the second term.)

By Ashleycrombie (Ashleycrombie) on Wednesday, April 23, 2003 - 04:18 am: Edit

x = 2 + squareroot18
or
x = 2 - squareroot18

By Ashleycrombie (Ashleycrombie) on Wednesday, April 23, 2003 - 04:21 am: Edit

i meant 2 +/- squareroot(-14) in both

By Brd (Brd) on Wednesday, April 23, 2003 - 10:14 am: Edit

Which is the same as Zerg's answer...

By Terpsfan (Terpsfan) on Thursday, April 24, 2003 - 03:28 pm: Edit

Excuse me but the only right answer is mr. pancake. Zerg is wrong because you cannot take the root of a negative number. Not only that but the root of 56 can be simplified. You all need to brush up on your math skills, and it makes me wonder how many people on these posts actually lie about their test scores....

By Dxiw (Dxiw) on Thursday, April 24, 2003 - 06:23 pm: Edit

zergs answer is right, it is simple an imaginary equation. That equation does not have any real solutions only imaginary ones. You solve using the quadratic formula:

ax^2+bx+c=0
a=1 b=-4 c=18

x=(-b + sqrt(b^2-4ac))/(2a)
x=(-b - sqrt(b^2-4ac))/(2a)

so...
x=(4 + sqrt(16-4*1*18))/(2*1)
x=(4 - sqrt(16-4*1*18))/(2*1)

so..
x=(4+sqrt(-56))/2
x=(4-sqrt(-56))/2
which when simplified is..
x=(4+2sqrt(14)i)/2
and..
x=(4-2sqrt(14)i)/2

for all you math morons, sqrt(56) = sqrt(14*4) = 2sqrt(14)

By Brd (Brd) on Thursday, April 24, 2003 - 06:24 pm: Edit

"Zerg is wrong because you cannot take the root of a negative number."

Um, sure you can. You have to admit what are called complex numbers. Apparently you have not learned about them yet, which is ok. If you will notice, Mr. Pancake also takes the square root of negative 56, he just simplified it and pulled out the complex factor i=sqrt(-1). But he forget to cancel the denominator in the second (imaginary) term so has an extra factor of 2 there.

Also, just to be pedantic, not simplifying something like sqrt(56) in an answer does not make the answer wrong. Not simplifying an answer might go against the instructions on some or other assignment, and cost you some "points", but that doesn't make the answer incorrect. Plug the unsimplified answer into the equation. You get zero. QED.

For the record, my second degree was in Mathematics. There are plenty of things I need to review; basic algebra is not one of them. :)

By Vizious (Vizious) on Thursday, April 24, 2003 - 06:44 pm: Edit

does x2 mean 2x or x^2

if x2 was viewed as 2x, the answer would come out to nine

By Brd (Brd) on Thursday, April 24, 2003 - 07:05 pm: Edit

Sure, but no one would ever write 2x as x2. If you were giving a talk at a seminar and did that I can gaurantee you dirty looks from across the room. I think the consensus is that x2 is an attempt to express x2 ("x squared" in case that didn't work) in a markup language with shoddy-to-nonexistant capability for mathematical expression.

Brd pines for the day that MathML is actually widespread enough to use...


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