hi im a newbie to mathes and have been doing calculus recently ive. Been given two formulas and need to differentiate themthem and solve the equation, ive had a good attempt at them. i would just like to confirm if they are corret.

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- Jun 24th 2010, 06:45 AMlukebushnellnewbie differentation
hi im a newbie to mathes and have been doing calculus recently ive. Been given two formulas and need to differentiate themthem and solve the equation, ive had a good attempt at them. i would just like to confirm if they are corret.

Attachment 17983 - Jun 24th 2010, 07:25 AMAckbeet
Your first one is incorrect, I think. Take the derivative first, without plugging in numbers. What do you get?

Your second one is confusing. I'm not sure what you mean on the LHS of the equals sign. - Jun 24th 2010, 07:31 AMGrandad
Hello lukebushnell

The first one is:

$\displaystyle \dfrac{ds}{dt}= -15e^{-1.5t}$When $\displaystyle t=0.7$

$\displaystyle \dfrac{ds}{dt}= -15e^{-1.05}$

$\displaystyle =-5.25$, correct to 3 s.f.

The second one is correct to 2 s.f. ($\displaystyle 2.21$ to 3 s.f.)

Grandad - Jun 24th 2010, 07:31 AMlukebushnell
hi , thanks for the quick reply,. sorry about the equation the bit befoere the = sgn should be i , because the answer is electrical current, and as for the first one im not sure on the answer, i cant rmeber from the exam. i thnik ill just have to wait to august to find out, but thanks for the reply , i appreciate it

- Jun 24th 2010, 07:34 AMlukebushnell
thanks grandad for the reply, that number does ring a bell but i have had so many numbers floating around my head so it could be any thing. :)