Question

in an ap the sum of first n terms is 5n2/2+3n/2 find its 20th term

Answer 1

Answer:

Step-by-step explanation:

Sn=5n2/2 +3n2/2

S1=5x1x1/2+3x1x1/2

   =5/2+3/2

   =8/2

   =4

S1=a1=4

S2=5x2x2/2+3x2x2/2

    20/2+12/2

    =32/2

    =16

S2-S1=a2

16-4=12

a2=12

a2-a1=d

12-4=8

d=8

a20=a+19d

     =4+19x8

     =156