1. Sep 18, 2005 #1

   IB

   

   Please help...
   
   Given U3 = 0
   S15 = -300
   How can you find d? And U1?
   
   (Instead of "T", we use "U" for "term", and d is the common difference)
   
   Thanks!

    

   Last edited: Sep 18, 2005

   IB, Sep 18, 2005
2. 
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3. Sep 18, 2005 #2

   IB

   

   No one can solve this problem? :(

    

   IB, Sep 18, 2005
4. Sep 18, 2005 #3

   Leong

   

   two simultaneous equations.
   one equation for each information given.
   solve the equations for a and d.

    

   Leong, Sep 18, 2005
5. Sep 18, 2005 #4

   IB

   

   Thanks a lot!

    

   IB, Sep 18, 2005
6. Sep 18, 2005 #5

   rocketboy

   

   Set up the 2 equations:
   
   Sn = n/2[2a + (n-1)d]
   Un = a + (n-1)d
   
   Substitute known values:
   
   -300 = 15/2 [2a + (15-1)d]
   -40 = 2a + 14d
   -40 - 14d = 2a
   a = -20 - 7d
   
   0 = a + (3-1)d
   0 = a + 2d
   a = -2d
   
   Set them equal to each other and solve:
   
   -20 - 7d = -2d
   -20 = 5d
   d = -4
   
   there's your d value bro....i'm sure you can do the rest!

    

   rocketboy, Sep 18, 2005
7. Sep 18, 2005 #6

   IB

   

   Yup, my bro's so smart!

    

   IB, Sep 18, 2005

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