Question

the first three terms of an a.p respectively are 3y-1 ,3y+5 and 5y+1 .then y equals

Answer 1

As
a =3y-1.
a2=3y+5
a3=5y+1
Now, Sn=n/2(an+a)
a+a2+a3=3/2(5y+1+3y-1)
3y-1+3y+5+5y+1 =3/2(8y)
11y+5=3(4y)
11y+5=12y
5=12y-11y
5=y
Hence, value of y is 5