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Math Crew: Help!

abhigames

Member
Messages
709
how would i derive a curve given that i know the function of another curve, the area between the curves and the area under the curve that I want to derive.... and obviously the total area under BOTH curves?
 

Havish

New Member
Messages
250
area under a curve is defined as the integral of the function. therefore if you integrate the function over the your limits, you should get the area under that curve. From there find the area under the curve you are trying to look for by subtracting it from the total area. Once you have that go backwards and take the derivative of that area to get the function of the curve.
 

abhigames

Member
Messages
709
VCU Bhangra and good at math....niceee...thansk dude...is that how guys make your formations...integrating and deriving the curves...sick.
 

abhigames

Member
Messages
709
by the way, here is a drawing of the curve with numbers

http://www.sendspace.com/file/lag9pz

dont know if that makes it any clearer
 

kinnell

*Account Deactivated*
Messages
2,159
MATH TEAM PRIDE. lol

Okay, here's the information from your pdf file: (I changed variable a to variable x)

f(a) = Top Curve = -x + 1
f(b) = Bottom Curve

Integral of f(a) = 0.5 (It's a triangle with intercepts at (0,1) and (1,0). Area = 1/2 (b) * (h) = 1/2

GIVENS
A = area between f(a) and f(b) = 0.2335
B = area between f(b) and axis = 0.2665
(A + B should = 0.5 and they do)

Now, f(a) is a straight line. f(b) has intercepts (0,1) and (1,0) and HAS to be at least polynomial. F(b) cannot be straight line and there should be a polynomial solvable equation. Anything more should need more information, so it's logical to assume that polynomial is answer.

Therefore, we can assume that it, f(b) = ax^2 + bx + c with solutions at least at (0,1) and (1,0)

f(b) = ax^2 + bx + c WITH inserted x
1 = c (x = 0)
0 = a + b + c (x = 1)

Then, a + b = -1 and a = - b - 1 OR b = - a - 1

Obviously, we need MORE information. Well, we know that the integral of f(b) from 0 to 1 equals the area of B which is 0.2665.

f(b) = ax^2 + bx + 1 (we know c = 1 now)
f(b) = ax^2 - ax - x + 1
Integral of f(b) = (a/3)x^3 - (a/2)x^2 - (1/2)x^2 + x = 0.2665
From 0 to 1, (a/3) - (a/2) - (1/2) + 1 = 0.2665
-(a/6) + (1/2) = 0.2665, a = 1.401
b = -2.401
c = 1

Thus, f(b) = 1.401x^2 - 2.401x + 1 = (1.401)b^2 - (2.401)b + 1 (in your units)
 

kinnell

*Account Deactivated*
Messages
2,159
I hope that helps. If you have questions on any parts, definitely let me know! I know that the variables got messy here and there, but its understanding the process that counts. :)
 

kinnell

*Account Deactivated*
Messages
2,159
HAHAHAH YES!

But respect Navkarn! Very few could make it sound like a legit song. I remember in Math Team, we made math raps about integrals, mysterious "e", little p (statistical analysis) and z-tests but alas, those were only raps and require no skill to sing.
 
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