Question

Find the sum of 10terms of an ap whose nth term is 1-4

Answer 1

Answer:

Step-by-step explanation:

an=4n−1

a1=a×1−1=3

a2=4×2−1=7

a3=4×3−1=11

d=11−7=7−3=4  

a=3

n=20

Sn=S20=n2[2a+(n−1)d]

S20=202[2×3−(20−1)×4]

S20=10[6+19×4]

S20=10×[6+76]

=10×82=820