June 23rd, 2012, 03:29 PM  #1 
Senior Member Joined: Jan 2012 Posts: 159 Thanks: 0  Related Rate Problem I keep getting the height to be 143 cm using similar triangles and differentiating. I am reading up on latex now to type up my steps. 
June 23rd, 2012, 04:07 PM  #2  
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: Related Rate Problem Quote:
the height of the boy : his distance from the spotlight :: the height of his shadow : the distance from the wall to the spotlight Letting h be the height of the boy, x be his distance from the spotlight, and s be the height of his shadow, h/x = s/1000. Hence . Substitute ds/dt = 46, dx/dt = 120, and x = 600, then solve for h.  
June 23rd, 2012, 04:46 PM  #3 
Senior Member Joined: Jan 2012 Posts: 159 Thanks: 0  Re: Related Rate Problem
thanks man my mistake was not treating 1000h like a constant which it is since it does not depend on time. THANK YOU! 

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