Question

if the sum of first n terms of an ap is 4n2- n2 ,what is the first term ? the sum of first two term?find second,third,10th and nth term​

Answer 1

Step-by-step explanation:

Sn = 4n^2-n^2

thus, S1= 4×1^2 -1^2

= 4-1

=3

and s1 = a1 so the first term is 3

S2= 4×2^2-2^2

= 16-4

=12

sum of first two term is 12.

a2 = s2-s1

= 12-3

=9

second term is 9.

Thus, AP is 3,9.......

a3 = a+2d

= 3+2×6

=15

3rd term is 15.

a10 = a+9d

= 3 + 9×6

= 57

10th term is 57.

an = a+(n-1)d is the nth term.