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[Iituem]

Trying to work something out, could use help.  This isn't for a test or anything, so I can ask for help ().

I need to solve for X:

1.5X + 0.3( ( (X-1)^2 + (X-1) ) / 2 )

I think this can also be phrased:

1.5X + 0.6( (X-1)^2 + (X-1) )

How can I solve for X?


[In this specific case, the question was 54 = 1.5X + 0.3( ( (X-1)^2 + (X-1) ) / 2 ), solve for X.]

[Vector]

No, okay, you need your equation to equal something.

3*18 = 1/2*3X + 3*1/2*1/10(X^2 -X)

360 = X^2 + 9X

X^2 + 9X - 360 = 0

And then you can hopefully take it from there.

[Darvi]

Besides, 0.3/2 is 0.15, not 0.6.

[Iituem]

Besides, 0.3/2 is 0.15, not 0.6.

For some reason I thought I was dividing by 1/2, not multiplying by it.  Bleh, too long since I schooled in math.

I think I might need to be walked through the logic here, though.


Edit:  Have gotten this far.

54 = 1.5X + 0.3( ((X-1)^2 + (X-1))/2 )

3*18 = 0.5*3X + 3*0.5*0.1( X^2 - X )  Divide by 0.5

108 = 3X + 0.3( X^2 - X )  Divide by 0.3

360 = 10X + (X^2 - X)

360 = 10X + X^2 - X

360 = 9X + X^2

9X + X^2 - 360 = 0

[Darvi]

9^2+4*360= 1521=39^2

x1=(39-9)/2=15
x2=-(39+9)/2=-24

Tadaa!

[Iituem]

9^2+4*360= 1521=39^2

x1=(39-9)/2=15
x2=-(39+9)/2=-24

Tadaa!

How did you get to that from 360 = 9X + X^2?  I'm still a touch lost.

[Darvi]

I just happen to know that kinda stuff.

[Iituem]

I just happen to know that kinda stuff.

Motherfrakkin' quadratic equations.  I remember hating these with a passion, no wonder I can't recall how to do them.  I've clearly blocked the memory.  ;P

(But seriously, thanks!  It's been a good 6 years since I last had to do anything like this.)

[Dutchling]

just use wolfram alpha for questions like this

Spoiler (click to show/hide)

[Muz]

Heh, quadratic equations pop up everywhere. They're like just a bit rarer than the usual statistics. One nice thing to pick up from school.