Example  	A rock is dropped into a well.  Three seconds later,                   the sound of the splash is heard at the top of the                  well.  How  deep is the well ?
 
Solution : Let h  be depth in feet of the well.  ( h  > 0 )
  
 
		Now td stands for the  time  it  took for the rock to fall down  and  tu stands for time  it  took  for  the  sound  reach up.
  
		Thus  td + tu  = 3 seconds
  
		Now h = 1100 tu,  since speed of sound in air is 1100 feet per second in all directions.
 
 
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       Index 
       
         4.1 Theorem 
        4.2 Definition 
        4.3 Methods of Solving Quadratic Equations  
      Chapter 5 
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