# Homework Help: Calculus Logarithmic Functions help please

1. Aug 2, 2010

### Moonflower

The question is:
A particle moves alonge the x-axis with position at time t given by x(t) = e^(-t) sin t for 0 ≤ t ≤ 2π.

1. Find the time t at which the particle is farthest to the left. Justify your answer.
2. Find the value of the constant A for which x(t) satisfies the equation
Ax" (t) + x' (t) + x(t) = 0 for 0 < t < 2π.

For no.1, I think its when t=0, because within the interval 0 ≤ t ≤ 2pi, 0 is when x has the least value, therefore most to the left.

For no.2, x(t)= e-t sin t, x'(t)= e-t (cos t - sin t), and x''(t)= -2e-t cos t. Factorizing, x(t)+x'(t)+x''(t) gives me e-t (sin t +cos t -sin t -2A cos t). To make the sums inside parentheses zero, A would have fit the condition 0= cos t - 2A cos t. A= $$\frac{1}{2}$$ fits, it seems.

Am I on the right track? Thanks
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Aug 2, 2010

### Filip Larsen

Re: Calculus Logarithmic Functions help please!!

For 1: Is there a way you can check if x(t) is a minimum for t = 0? How would you normally find a minimum of x when you have access to the derivatives x' and x''?

For 2: Looks correct.

3. Aug 2, 2010

### Moonflower

Re: Calculus Logarithmic Functions help please!!

aah, i didn't think about that..thanks!