luqmanwar123 luqmanwar123
  • 25-04-2018
  • Mathematics
contestada

a8= 40 and a13= -10, find a1 and d

Respuesta :

jamuuj jamuuj
  • 06-05-2018
A term in an arithmetic progression is given by the formula a1 + (n-1) d
Thus; a8 = a1 + 7d =40 
         a13 = a1 + 12 d = -10
Solving them simultaneously;
   a1 +7d =40
  a1 + 12d = -10     subtracting the two equations
          -5d =50
             d = -10
   a1 = 40 - (7× -10)
        = 110
Therefore; a1 = 110 and d = -10
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