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Off-Topic Discussion => General Discussion => Topic started by: kasperl on June 19, 2005, 10:44:33 am

Title: Algebra help required.
Post by: kasperl on June 19, 2005, 10:44:33 am

The following problem is given:

fa(x)=ax^2
g(x)=x^3

The area enclosed by fa(x) en g(x) has a size of 12.

Calculate a.

Ok, this is in the chapter explaining integrals, so you have an idea what stuff this is.
I can state
(capital F means 'primitive function of f')

Fa(x)=(a/3)x^3
G(x)=(1/4)x^4

So now I get:
Fa(x)-G(x)=12
(a/3)x^3-(1/4)x^4=12

And I've got a system with 2 unknows, which I cannot solve.

Help would be appreciated, exam is tommorow.


EDIT: If I realise that fa=g on the intersection, I can write out ax^2=x^3 so x=a, and I can integrate:

12=(F(a)-F(0))-(G(a)-G(0))

/me is stupid.


Anyway, you guys CAN help me by devising more problems more or less like this one. Try to make them hard, but solvable. If no-one can think of anything, the admins can close this.