1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Related Rates - Trig

  1. Nov 10, 2012 #1
    1. The problem statement, all variables and given/known data

    If theta increases at a constant rate of 3 radians per minute, at what rate is x increasing in units per measure at the instant when x equals 3 units?

    3. The attempt at a solution

    I drew the triangle and I came to the conclusion that I needed to use 5sin(theta)=x

    Then I did the derivative and it comes out to 5cos(theta)d(theta)/dt=dx/dt

    Here is where I am a little confused, I get cos(theta) = (5/2)√(3)/5 based off of the 30 60 90 triangle.

    Am I doing this right? After I do the calculations, I don't get the right answer because no where are you supposed to have a sqrt in the answer.
     
  2. jcsd
  3. Nov 10, 2012 #2

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Please write the complete problem as it was given to you.

    I may be able to guess what you're supposed to do, but if my guess is wrong, that won't really help you.
     
  4. Nov 10, 2012 #3
    I typed the problem word for word, I'll include the multiple choice answers in this post:

    a) 3
    b) 15/4
    c)4
    d)9
    e)12
     
  5. Nov 10, 2012 #4

    Zondrina

    User Avatar
    Homework Helper

    This is a related rates problem right? What is dθ/dt? What is dx/dt? Write down all your variables BEFORE you start trying to manipulate things.
     
  6. Nov 10, 2012 #5

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    If you typed it word for word, as follows, copied & pasted directly from your Original Post, & shown below:
    "If theta increases at a constant rate of 3 radians per minute, at what rate is x increasing in units per measure at the instant when x equals 3 units?"​
    then, where does the triangle come from, about which you stated:
    "I drew the triangle and I came to the conclusion that I needed to use 5sin(theta)=x"​
    ??
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Related Rates - Trig
  1. Related rates formula (Replies: 3)

Loading...