# Math Help - newbie differentation

1. ## newbie 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.

2. 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.

3. Hello lukebushnell

The first one is:
$\dfrac{ds}{dt}= -15e^{-1.5t}$
When $t=0.7$
$\dfrac{ds}{dt}= -15e^{-1.05}$
$=-5.25$, correct to 3 s.f.

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

Grandad

4. 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

5. 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.