Question

If first term of an ap is a second term is b and last term is 2a then find the sum of the all terms

Answer 1

a1=a

a2=b

d=a2 - a1

d=b-a

an = 2a

a +( n-1)d = 2a

Subsituting value of a &

a + (n-1)b-a = 2a

(n-1)=a/b-a

n = a/b-a + 1

n=b/b-a

Sn = n/2(a + an)

=b/b-a/2(a + 2a)

=b/2(b-a)×3a

3ab/2(b-a)