# Using chain rule to obtain the derivative dz/dt

1. Nov 3, 2015

### catch22

1. The problem statement, all variables and given/known data

2. Relevant equations
dz/dt = dz/dx⋅dx/dt + dz/dy⋅dy/dt

3. The attempt at a solution

I am getting :

=[-sin(x+7y) ⋅ 10t] + [-sin(x+7y) ⋅ 7 ⋅ (-1/ t2)]

then changing x and y terms:

=[-sin((5t2)+7(1/t)) ⋅ 10t] + [-sin((5t2)+7(1/t)) ⋅ 7 ⋅ (-1/ t2)]

2. Nov 3, 2015

### Ray Vickson

Do you have a question?

3. Nov 3, 2015

### catch22

yes, sorry, I'm just verifying If I had done it correctly.
the answer my teacher posted was :

which really got me questioning myself.

4. Nov 3, 2015

### Samy_A

It seems that you teacher has $x(t)=5t^4$