Question

7th term of an arithmetic sequence is 15 and 13 term is 27 . find 20th term​

Answer 1

Answer:

a

7

=15=a+6d....(1)

a

13

=27=a+12d...(2)

Subtracting eq

n

(1) & (2)

a+6d=15

a+12d=27

__________________

−6d=−12

d=2

Putting in eq

n

(1), we get ;

a+6d=15

a+6(2)=15

a+12=15

a=3

∴n

th

term =a

n

=a+(n−1)d

3+(n−1)2

⇒3+2n−2

Answer 2

Answer:

20th term=41

Step-by-step explanation:

nth term=a+(n-1)d

15=a+6d-equation 1

27=a+12d- equation 2

multiplying eq 1 by 2 and subtracting it from eq 2

we get

a=3

by substituting the value of a in eq 1 or 2

15=3+6d

d=2

20th term=3+19(2)

=38