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**Titus****Member**- Registered: 2005-03-07
- Posts: 10

I can't work out the derivative for this equation;

P = 2t³/3 + t² - 40t - 5

and then i need to find what 't' is when the derivative of the above equation = 0.

Any help would be great.

Thanks!

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**numen****Member**- Registered: 2006-05-03
- Posts: 115

Generally speaking,

The left side is your derivative. Does this help or should I give you some hints?

When you've got the derivative, set it equal to 0 to obtain your equation, then solve for t.

Bang postponed. Not big enough. Reboot.

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**luca-deltodesco****Member**- Registered: 2006-05-05
- Posts: 1,470

and ofcourse

if f(x) = a0(x) + a1(x) ... an(x);

f'(x) = a0'(x) + a1'(x) .... an'(x);

so

P(t) = 2t³/3 + t² - 40t - 5

P'(t) = **2t² + 2t - 40** = 0, 2(t+½)² = 40½, (t+½)^2 = 20¼, t = -½ ± √(20¼) = -½ ± 4½, **t = 4, t = -5**

*Last edited by luca-deltodesco (2006-08-22 08:08:39)*

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