Question

find the sum of first 30 terms of an AP. whose nth term is given by an=7-4n​

Answer 1

$\huge{\boxed{\mathtt{\purple{Answer}}}}$

An=9-4n
if n=1 ,then A1=5
if n=2,thenA2=1
So d=A2-A1=-4
S30=n/2[2a+(n-1)d]
=30/2[2 x 5 +(30-1)-4]
=15[10+(-116)]
=15 x (-106)
=1590