# Need Immediate help, stuck on 2 calc problems

• Aug 30th 2012, 10:11 AM
Elonzos
Need Immediate help, stuck on 2 calc problems
1. find dr/d (theta)
r=4-theta^2sin(theta)

and

2.Let x and y be differentiable functions of t, and let s=sqrt(5x^2+y^2) be functions of x and y.

a. How is ds/dt related if y is constant
ds/dt=?dx/dt

b. how is ds/dt related to dx/dt and dy/dt if neither x nor y is constant
ds/dt= ? dx/dt+?dy/dt

c.How is dx/dt related to dy/dt if s is constant
dx/dt=?dy/dt.

HAVE NO IDEA AND NEED HELP, PLEASE AND THANK YOU
• Aug 30th 2012, 10:41 AM
Prove It
Re: Need Immediate help, stuck on 2 calc problems
Quote:

Originally Posted by Elonzos
1. find dr/d (theta)
r=4-theta^2sin(theta)

and

2.Let x and y be differentiable functions of t, and let s=sqrt(5x^2+y^2) be functions of x and y.

a. How is ds/dt related if y is constant
ds/dt=?dx/dt

b. how is ds/dt related to dx/dt and dy/dt if neither x nor y is constant
ds/dt= ? dx/dt+?dy/dt

c.How is dx/dt related to dy/dt if s is constant
dx/dt=?dy/dt.

HAVE NO IDEA AND NEED HELP, PLEASE AND THANK YOU

1. \displaystyle \begin{align*} r = 4 - \theta ^2 \sin{\theta} \end{align*}

This is a product of functions, so to differentiate you need to use the product rule.

2. a) Use implicit differentiation.

b) Use implicit differentiation.

c) If s is constant, its derivative is 0. But you will already have ds/dt from part b), so this will equal 0. You can then see how dx/dt and dy/dt are related.
• Aug 30th 2012, 10:52 AM
Elonzos
Re: Need Immediate help, stuck on 2 calc problems
Thank you but I keep getting a red mark (wrong) when I do it so I'm not sure of the actual values. I worked them out several times. I think I need step by step solution
• Aug 30th 2012, 12:05 PM
HallsofIvy
Re: Need Immediate help, stuck on 2 calc problems
You get a "red mark" so you are submitting these for credit?
• Aug 30th 2012, 07:57 PM
Elonzos
Re: Need Immediate help, stuck on 2 calc problems
No, these are practice but they suppose to be real similar to the actual test. The test is tomorrow and it's timed. 60mins So I'm trying to learn it now.
• Aug 30th 2012, 08:31 PM
Prove It
Re: Need Immediate help, stuck on 2 calc problems
Quote:

Originally Posted by Elonzos
Thank you but I keep getting a red mark (wrong) when I do it so I'm not sure of the actual values. I worked them out several times. I think I need step by step solution

You won't get a step by step solution. If you post what you have done, then we can tell you where you have gone wrong.