Question

if nth term of an A.P is 4n+3 then find 1. 20th term 2.Form A.P 3. Find sum of first n terms
class 10
Arithmetic Progression
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Answer 1

Step-by-step explanation:

since nth term of AP = 4n+3

=> 20th term = 4×20+3 (put n =20)

= 80+3

= 83

Therefore a20 = 83

1st term (a) = 4×1+3= 7

2nd term (a+d)= 4×2+3= 11

3rd term (a+2d)= 4×3+3 = 15

common difference= 15-11 or 11-7

d = 4

=> AP = 7, 11, 15 ,19, 23............4n+3

sum of first n terms= (n/2)(a+l)

= (n/2)[ 7+(4n+3)]

=(n/2) ( 4n+10)

= n(2n+5)

=> Sn = n(2n+5)

hope this helps you