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November 11th, 2012, 04:55 PM  #1 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  A particle moving around a circle and a point
Problem says: A particle is traveling around the cirlce x^2 + y^2 =25 where x and y are measured in inches. At the instant the particle is at the point (3,4), dx/dt = 7/sec. Find dy/dt at this time ??? 
November 11th, 2012, 05:11 PM  #2  
Math Team Joined: Jul 2011 From: North America, 42nd parallel Posts: 3,372 Thanks: 233  Re: A particle moving around a circle and a point Quote:
Divide out the constant 2, then plug in, there is only one unknown so you can solve for it.  
November 11th, 2012, 05:19 PM  #3 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: A particle moving around a circle and a point
wait do I take the dx or the dy over to the otherside of equation and then divide by 2? please show me so I can use as a key for future problems 
November 11th, 2012, 05:23 PM  #4 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: A particle moving around a circle and a point
wait I think I c so 2y dy/dy = 2x dx/dt dy/dt = x dx/dt = dy/dt = 3 dx/dt dy/dt = 3(7/sec) dy/dt = 21 inches/ second holy ***** sh** its a miracle 
November 11th, 2012, 05:35 PM  #5 
Math Team Joined: Jul 2011 From: North America, 42nd parallel Posts: 3,372 Thanks: 233  Re: A particle moving around a circle and a point
Did you confirm the answer in the back of the book? You made a small error, let's see if you can find it. 
November 11th, 2012, 05:37 PM  #6 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: A particle moving around a circle and a point
no even problems not in back of book I don't see the error tell me please 
November 11th, 2012, 05:43 PM  #7 
Math Team Joined: Jul 2011 From: North America, 42nd parallel Posts: 3,372 Thanks: 233  Re: A particle moving around a circle and a point
mathkid, your work is only 5 lines, please check your work. You made an error in line 1 which you corrected in line 2, but you made another error in line 2. 
November 11th, 2012, 06:04 PM  #8 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: A particle moving around a circle and a point
ok Agent and TY for staying on me I c it 2x dx/dt + 2y dy/dt = 0 2y dy/dt = 2x dx/dt y dy/dt = x dx/dt dy/dt = x/y dx/dt dy/dt = (3/4)(7/1) dy/dt = 21/4 = 5.25 in/sec 
November 11th, 2012, 06:23 PM  #9 
Math Team Joined: Jul 2011 From: North America, 42nd parallel Posts: 3,372 Thanks: 233  Re: A particle moving around a circle and a point
Very good [color=#0000BF]mathkid[/color], i wouldn't be helping you learn if i simply handed all answers to you, I thought in this particular case you were capable of spotting your error if you took the time to go over your work. Spotting our own errors is a very important procedure when learning mathematics of any level. 
November 11th, 2012, 06:26 PM  #10 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: A particle moving around a circle and a point
TY I PROMISE I AM TRYING GOING ON 6HRS NOW WITHOUT MUCH OF A BREAK 

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