Question

if the nth term of an ap is( 4 n+ 1) find the sum of the first 15 term of the AP also find the sum of The n terms

Answer 1

1st term = (4*1 +1 ) = 5
2nd term = (4*2+1) = 9
d = 9-5 = 4
S15 = 15/2 ( 2*5 + (15-1)4 )
= 15/2 ( 10 + 56)
= 15/2 (66)
= 15 *33 = 495