Question

tn=10-3n find s40 tn=10-3n find s40​

Answer 1

ANSWER

tn=10-3n

T1 =10-3[1]

    = 10-3

    =7

T2 =10-3[2]

    =10-6

    = 4

d = a2 -a1

   = 4-7

   = -3

Sn = n/2 [ 2a +  [n-1] d

S40= 40/2 [ 2 {7} + {40-1} {-3} ]

      = 20[14+ + 39{-3}]

      = 20 [ 14 + {-117} ]

      = 20 [ -103 ]

      =-2060

 hence answer is -2060