Question

find the first term and the nth term of an AP whose 6th term is12 and 8th term is 21​

Answer 1

Answer:

tn= (a+(n-1) d)

t6= a+(6-1)

a+5d=12 (1)

t8= a+(8-1)d (2)

a+7d=21

subtracting (3)-(1)

2d=10

d=5 a+5d=12

+2=a+(2-1)d a+25=12

a=12-25

=-13+5=-8

tn=a+(n-1)d

=-13+(n-1)5

= -13+5n-5

5n-18