Question

Plz solve it. It is question of 10th class.

Answer 1

1. an=3+4n

n=1

A1=3+4(1)

A1=7

n=2

a2=3+4(2)

a2=11

.d

,D=a2 -a1

d=11-7

d=4

Sn=n/2(2a+(n-1)d)

S15=15/2(7(2)+(15-1)4)

S15=15/2(14+56)

S15=35*15

=525

part. 2.

an=9-5n

a1=9-5(1)

a1=4

a2=9-5(2)

a2=-1

d=a2-a1

= -1-(4)

=-5

now, S15=15/2(4(2)+(15-1)(-5))

=15/2(8+(-70)

=15/2(-62)

=15*(-31)

=-465