Question

If an= 5n-2 find its first term , common difference and 21st term

Answer 1

put n =1

an = 5(1)-2 = 5-2 =>3

put n =2

an=5(2)-2=10-2=>8

put n=3

an=5(3)-2=15-2=>13

Now,

3,8,13,....

a = 3 d=a2-a1 =>8-3=5

similarly

d=a3-a2 =>13-8=5

formula :-

an= a+(n-1)d

a21= 3+(21-1)d

a21=3+20 d

a21=3+20(5)

a21= 3+100

a21=103

••• therefore a21=103

this will help you